Trundle is probably one of the most overlooked champions out there. Reason being is that he is one of the slower junglers out there, and he can't really lane well at all. Nevertheless, If you need a jungler, that might require a little skill to play, but ends up becoming a fairly decent carry later on, Trundle is your troll.

Runes are slightly odd on Trundle, I take Greater Mark of Desolation, Greater Seal of Armor, Greater Glyph of Scaling Cooldown Reduction, and Greater Quintessence of Health. These help speed up the jungling process in the beginning, and still have enough HP left over to gank a lane of your choice. A Guide on where you can start will be posted in the Jungling section.

There are a lot of Builds for Trundle, but for this specific build, I do 2/18/10. I take the basic Defensive masteries in defense, with improved Exhaust and Smite , and putting two points in Utility Master.

I take Smite for obvious reasons, and I also take Exhaust because Trundle's job later on, becomes taking out your opponent's AD carry. Honestly, with exhaust and his ult Agony it's fairly easy to disable them, even if you can't kill them. With Contaminate and Mercury Treads, You rarely ever need Ghost. Plus the Pillar of Filth, can help you escape or catch up. . .

This is pretty straight forward, You want to take Rabid Bite and Agony whenever possible, because those are your only attacks. You put one point in Pillar of Filth at level 4, for ganking and escaping purposes, and max Contaminate right after Rabid Bite.
There really isn't a real reason to try to change the build at all, because you can make up for it in your item build.

The item build is pretty much exactly as follows at the top. Only thing is, and I can't stress this enough, ALWAYS BUY WARDS!!! They are fairly cheap and the pay for themselves. Since you are the jungler, you are responsible for map control.

This build is probably one of the more cheaper builds out there, at 12920+wards and potions. More often than not, Other guides tell you to get B.F. sword items, or other things like Trinity force. While they are good items for Trundle, the reality of it is he can't farm too well, and don't have the time to get 17-18k gold.

Also one more thing, I've recently started trying out Tiamat. Personally, I really like it. Especially in team fights. . . Since your only Direct damage spell is Rabid Bite, You need to make up for it by taking some splash damage. Now your single target attack and your basic attack has become a AoE attack. Also, It procs on your Wriggle's Bonus minion damage, so there's a 20% chance for you to do 700 damage to a minion, AND do about 350 damage to everyone around it.

If the game goes on for a while and you've got all six of your items, and you still have money to spend, Sell Wriggle's Lantern, for a Black Cleaver. Otherwise They are just plain too expensive.

One note worthy thing about jungling with Trundle is most people to it wrong. You should cast Rabid Bite as soon as you hit with your basic attack. This increases your DPS significantly, and take less damage from monsters.

You should always start at the wolves. You should kill the big wolf, with just rabid bite, then immediately leave for blue Golem. Down it with Rabid bite and smite, you will need to use a Potion here. Go back and kill the two remaining Wolves, and head for small golems. Once you've killed them, You should be able to take Red buff with Smite, Rabid bite, and Contaminate. Of course using pots in between camps to maximize survivability. Afterward, you can go gank a lane, or if your team isn't ready, kill wraiths and go back. From there, you should just get on a regular cycle, taking blue, red and dragon as soon as they come up.