This guide is about teaching you how to jungle with singed, not to pesuade you to play him.
If you like singed, his abilities and plays-tyle go read else no need. I wont get offended.

Singed has a unique game style that is much more fun to play with.
All the junglers that take Wringles Lantern wringles lantern and are based on autoattacks are so boring!!!
These champs are only for players that dont need any skill and just know to push the right botton of the mouse XD.
Besides, jungling phase is over after 15-20 min mark and the usual junglers like shaco+lee+fiddle etc..., are loosing their strenghs. But Singed not at all. He is dominating through the entire game. Even vs fed champs, Singed just lough at legendary heroes in their face.

For the best information about singed's skills+history hover your mouse over the icons at the begginig of this guide or go to these websites.

http://leagueoflegends.wikia.com/wiki/Singed_the_Mad_Chemist
http://eune.leagueoflegends.com/champions/27/singed_the_mad_chemist

It must be better than to copy paste over here.

Lets figure it out what is the best build for singed (including everything not just the items)...
You can look at it as pros and cons also :)

Here are the facts.
Most important to mention is his passive. Singed life bar scales with maximum mana. In generally always try to benefit from your champ passive as much as you can. Its preety silly to restore health to nasus through potions and health regan and not through hitting (he has quite a big amount of free life steal :)
Exept for poison all his abilities have rather high colldown
All of his abilities cost lots of mana.
He scales only with ap.
His damaging abilities have no range at all.

So as you can expect the build we better give to singed is better be a mix of ap, mana, speed and tank. Cooldown reduction is less important but always helps.
Ap is important to deal damage! Singed scales vey well with ap.
Tankiness is needed to be able to get to melee range for the fling and to inflicted the poison to the enemy even to those in the rear of the fight.
Mana is neede to benefit from his passive and to make sure he dont run out of mana.

Warning!!!!!!!!!!!!!!!!!!
Dont go on any one (total ap/total tank) extremly. Like the attractive ap build (people tend to like damaging builds). Belive me untill you will fling one of them you will miss lots of health and you will have to retreat soon after. If you want a total ap build while jungling just play fiddle, karthus, cho'gath etc...

Runes+Masteries+Skills Sequence are obvious. Dont take others!

Singed is a melee type of mage so he needs the tankiness and speed.

Fling is only made for flinging, its cooldown is too high to do a good amount of damage consistently. For damaging we have poison maxed, it has no cooldown at all.

***The question needed to be asked is if to go 9 21 0 or 0 21 9.
Well i tend to go with the 9 points in offence because it speeds up the jungle and singed doesn't need the early mana or any other skills from the utility tree. Well maybe the speed boost can be usefull but its only 2% for 4 points!!!!

Summoner spells are obvious as well. Dont take others!
Use smite as often as you can (free 10 gold). if you think baron or dragon or your buffs will be challanged save them.
Use ghost whenever you need more speed! Especially if you want to gank before lvl 4 or before you have shoes else you will catch no one.

Now items. Here i can start to explain!!! :)
Start with cloth armor and 5 pots health pot and continue as i showed (if you dont have the whole money for the big item build parts of it). Only thing that might be considered is to upgrade Glacial Shroud into Frozen Heart before Rylai's Crystal Scepter depends if their carry is fed or if they team is mostly containing ad champs.

Now why i build it like that??? Because unlike in lane the jungler gets damage from creeeps always and in addition he is levels behind some other champs. So most important thing to get is health+health regan else you will recall every 2 min and its not practical! So rush with this build untill you get force of nature!!! After this item you will laugh how your health is always full and how the damage that was taken by you is so neglectible. :)
Those items Force Of Nature and Rod Of Ages aren't cheap and untill you'll get them armor is also needed. So ninja tabi will do the best job, so get it!!! Its also the cheapset level 2 boots wich desparetly needed for good ganks.
Rest of the items are ovious.
And dont buy more magic resist or armor! by the time you get more of those types of items enemy will have some sort of 40% pen so they will be useless and waste of money.
Another thing to consider is, after you get glacial shroud you can change ninja tabi to mercury threads but i never did that because Singed allready has 10 tenancy from masteries + 20 tenancy from ult wich were enogh for me.

Start from: Wraithes -> Red buff (use smite ) -> Small golems(stand behind the small and fling the big one so poison will affect them both and kill the big one first!!!) -> Wraithes (they will respawn) ->Wolves (use smite smitesize=55 again).
End of round one, recall and buy Ruby Crystal youll have exactly 475 gold for it.
After it while you still have red buff do: Wraithes -> Wolves -> Blue buff (use smite and give it to someone else!!!)
Now you are lvl 4 take the slow (w skill), kill any other creep camp to get 350 gold, then recall and buy shoes. From here you can gank eazily!!!!!!!!!!!.

Take note to stand in the middle of the creeps so your poison will inflict them all.
I find that pulling is not helping me. So you may tell your team not to pull the creeps but only to damage them a little.
This link will explain how to do it http://www.youtube.com/watch?v=KFOiRATS0KI !!!
Its called: "Jungle Singed, level 4 in 3:24 without leash."

Singed never needs any buffs except for the red buff at start. If anyother buffs are availble give them to your ap mage (for the mana) or ad carrie (for the slow). If you take it you gain nothing worth mantioning while the chmaps i mentioned earlier will benefit from them a lot.

Team work is a little bit complicated and needs practice!!!
First of all you go first if the teamfights. If your team fights without you or not wa8ing you its gg you have a bad team!!!
Now lets explain each situation possible.

1) All teams are together at mid /near baron/ one under turret and one pushes.
In this case the tanks are infront and the rest are poking behind them.
get close and bait them to hit you!!! They will try to hit you and if someone is to close put the slow field and fling them or get closer and only fling them (the slow field have a decent animation time!!!). It will work eventually. Do it again and again.
By doing this you will draw the fire, waste their mana and you wont get any damage almost while your team will poke them as well.
If the teams are even (a good way to check that is to look at the kill score) your team have the adavantage.
Pop ult and Poison Trail poison trial and run to their carries while poisoning all enemy cahmps in your way.
Dont let their carries to shoot your team!!! Hit them and fling flingsize=55 them back from the fight so they will have to walk back and if they are noobs they will start to shoot you after you fling them :) !!!
Put slow field on top of enemy team to prevent them to reposition or chase your carries or to separate their team during the fight.
All the time run between the enemy champ and poison them and fling+hit the carries.

2) Gnking. You see a lane that is pushed just run to it. Try diferent directions in case one directin is warded. If you can catch them, fling them back and use slow field afterwards to catch the second enemy if there is another.
If you cant catch them put the slow field poisonand hit them and when they are getting out of it fling them to maximise the slow field ability. You always have ghost+ult to ***its you in speed isssues.

3) You have disadvantage. Maybe cause enemy is stronger or you are 3 vs 5. so help your team escape. you have yourself and the slow and the Fling . Use them wisely they have pretty long cooldown!!!

Dont forget you want enemy team to focus you you are tanky you take less damage and dont do to much damage. So i recommend always to get some damage done to you till you are 50 percente and charge in. this will bait them to hit you even more while your team will rip them apart. Your ult insanity poton armor magic resistance and hp refan will keep you safe.

Youll need this techniks to juke Frozen Mallet champs the rest of them are eazily juked by just running and put slow feild on you.

1) If you run to your base and someone is infront of you just fing him behind and continue as usuall.

2) iI hey flashed/dashed over your slow field just run back to your slow field and w8 untill they step on it again (they will come back or else they cant hit you) and continue to run (the slow field still efects for 1 sec even after they left it). Anyway you can fling them back anytime into it again.

3) They are many of them or you are low on health. Pop ult and ghost now even 5 enemies cant stop you. You will just run trough them and their stuns/snares/slows are almost uselessagainst you. Put the slow feild on top of you and run home. If alistar or lee walk before you to throw you back just fling them to the side! Dont w8 untill its to late, you will reagret it!! :)

Rush my items till Force of Nature . This means you must get kills or lane creeps. From jungling itself it will take forever!!!!!!!!!!!!
So gank, gank and gank when you see the opurtunity even in low health. Just by going towards them, you will scare them what will make them run and ezier to be killed. Your poison and slow from w skill will give you the ***its money that is needed for the items.

Extremly important!!!
Only if your ult is not on cooldown!!!
If a lane is with creeps and no one have the guts to farm it. Maybe cause it is extended to enemy 2 or 3 turret go on that opurtunity and farm it with the poison untill you reach the turret. You are unkillable Singed.
This will increase your gold income drastically!!!!!!!!!
If enemy will comes look at juking chapter. :)
If enemy push a turret leave it and let your team defend it. 4 champs+turret should hold eazily 5 enemy champs. Meanwhile you push and farm another lane. This will take you 1 min the most and youll make the enemy team to come back what will free your team from defending.
Do this untill force of nature. After that item youll become so much more dominant and you can really be with your team and help them and own teamfights.

Singed is "the champ" while his ult is active (just like master yi). There is a good reason y riot gave him 25 sec ult and y masters yi ult refresh when he kills!

After youll get 6 youll be much stronger faster and resilient to damage. While your ult is activable (not on cooldown) dont be afraid of counter jungling go to their base and take buffs+creeps, push lanes. You can run to where-ever you want.
After 6 dont be afriad of strong champs and even champs that are 4 or 5 lvl a head of you go fling them and they'll automatically run to their team even if you are alone!!!

If a problem came look at juking chapter. :)

Dont use your ult for hp/mana regan just recall and save the ult for ganks and escapes!

Extremly important!!!
Take care especaially from mid champs. Most of the times their combo can kill an enemy ap carrie and Singed does not have magic resist per lvl just like mid champs. So if they can kill a 6 lvl mid champ with their combo and youll come to gank them with a level lower than them youll just die really fast!!! So i dont recommend to gank mid if the y are above 6 and you are not 6 at all. Gank them if they are less than 6 or if you are 6 or above as well.

Save smite for the small golems and buffs crepps while jungling. They do most of the damage to you, rest of the creeps die really fast.

Take care from Frozen mallet champs. they are harder to escape even with the juking techniks i thought.

Another good tip is to leave your poison trail on while ganking. Its hard to tell if its on or off especially while ult is active. The ult looks and sounds like poison trail. :)
sometimes i turn it on and it doesnt go and i miss tons of ***its and it makes me look so stupid. XD
After Rod Of Ages , poison trail doesn't consume any mana almost so leave it on during fights!!!

And i will finish as i said before. Say to your team to w8 for you, if they fight withour you its gg. you have a bad team!!!!!!!!!!!!!!!!!!!!!!!


And dont forget to sing the song: Jungle Singed, jungle Singed. Does whatever jungle Singed does... XDDDDDDDDDDDDDDD

Good luck and go get them sommuner !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!