Well This is my very first guide.
I just wanted to make a simple, and short guide about Singed who is one of my favorite chars in LoL
I took the Singed Guide by Keels as sort of a basis for this one just that i changed a few things ( different late game items, masteries,...)

Pros:

Great Chaser
Great Escaper
Hard to kill
pretty nice in team fights if fling is used well
feeds good on assists and kills

Cons:

pretty weak early game
no ranged attacks
not easy to haras with him
has a few Nemmesis Chars ( Morgana YOU ***)

Quints

Greater Quintessence of Movement Speed are my first Choice, but you can go aswell for flat Hp or Ap

Marks

Greater Mark of Magic Penetration so he hits a bit harder
I wouldn´t recomend any other marks

Seals

5x Greater Seal of Armor and 4x Greater Seal of Defense for a bit more durability. You can aswell go just for the Resilience makes nearly no difference

Glyphs

5x Greater Glyph of Magic Resist 4x Greater Glyph of Scaling Magic Resist
Same as with the Seals

well my Masteries are
1/21/8
Which turns you into a really unstopable force
especially Juggernaut turns you into a Juggernaut :)

I didn´t take Durability into the build cause i Prefer to have more defense then to have more live
the 8 points in utility are for getting the 2% mov. speed
and the last point in the off tree is for Summoners Wrath so can get the maximum out of Ghost

you can go for 9/21/0 aswell but i prefer to be faster then to do a bit more dmg.
And the reason why I diddn`t take the 1/8/21 maserties is cause I think its more important to be able to stay longer in the lane with the def masteries instead of having 30 secs reduced cd on ghost. With a good thrown Mega Adhessive you can catch most of them without ghost and your Insanity Potion should be enough to get em

the Core Items are

Rod of Ages for a Pretty nice bonus health/mana and AP
Force of Nature a nice Health regen, Movementspeed and as a Bonus some magic resist
Rylai's Crystal Scepter More health a very pratical slow and a bit of damage.

Boots

Mercury's Treads are my first Choice
Ninja Tabi Against very have AD teams which dont have a lot of CC
Boots of Swiftness another good choice if you want the extra movement but with Ghost and Insanity Potionyou should be fast enough when necessary
and if you are already owning your enemies and dont know what to do anymore just get Sorcerer's Shoes for a bit more dmg

My choices for the last 2 Items are usually

Zhonya's Hourglass and Abyssal Mask

other options depending on the enemy team are

Rabadon's Deathcap DÄÄÄMAGE
Guardian Angel Armor and Magic res and you all know the annoying Passive
Lich Bane for even more Movment, a bi tof AP and a nice bonus autohit
Thornmail if the enemies have very strong AD champs. Makes them kill themselves
Banshee's Vail WEll you are allready unstopable but with this they wont even bother to target you anymore
Randuin's Omen against AD with a nice passiv
Frozen Heart Pretty mch the same as Randuins but with CD reduce

: Your most important Spell. Max it First cause this is were nearly all your damage comes from.
Don't forget to turn it on/off at the right time or you will be Oom very quickly (at least in the early game)

: I max this second cause its a really good spell to escape and catch someone. and the Higher the rank the stronger it gets.
The best way to wse it is to put i right under the place where you throw someone so your allies have enoigh time to get him. The other ust is to slow them in front of you so you can get to them and fling them. And last but not least when escaping.

: Fling is a really nice spell but you will max it last cause you only need the throw of it and not the damage

: You want to get Insane? Use it! Whenever you have to escape and they are catching up, in every team fight when you get focused and finally if Ghost isn't ready and you have to chase.
You will get really tanky, a bit faster and your Poison will do more damage.

well thats it for Now i will still change things, add things but if you want more info just look up This Guide by Keel. Except for the differencesin the masteries and the Item build I completely share his opinions and there is already all the info I have to add yet

and if somebody can tell how the hell the tables in BB code work i would be happy :D
and thx to Searz who helped me a bit with the BBCode through this site