I usually jungle Diana, maybe Jax or Olaf if we already have someone taking solo top.

Diana just because of her fast clear times, durability from minions due to her refreshing shield, and being such an "in your face" champion. Also she is really fun to play

Skarner and Lee Sin imo

Nunu is the best jungle. Do not listen to these people....
Build him correctly as an AP tank then your team will own!
Not to mention he has consume which acts like a smite and heals you.

Skarner is prolly the best all around but shaco is also insane, the problem with shaco is people dont know how to play him even though they will never believe this.. =[ but sadly its very true even the people who post shaco videos on youtube still play him badly =[

btw shaco counters nunu hard

Maokai and Skarner are my personal favorites.

Maokai ganks are insane. I love rolling in and then waking them backwards with my q. I find him pretty epic during team fights. His ult is great, assuming you can keep people in it. His Saplings act as 35 sec wards. My favorite junglier by far.

Skarner is fun as well. His ganks are great, but not quite Maokai level. That slow is fun, and his ult if you get it is hilarious. I build him and Maokai about the same and find Mao a little tankier. Can't go wrong with either really.

I personally am a fan of playing the Tank/Jungler, they just have such good sustain and often very good at ganking. I tend to play jungle Amumu or Maokai because with their abilities ganking can be a sinch since you can stun, snare or slow. Hope this helps people out

Ww is just the beginner choice... works decently.
Lee Sin, Amumu, and Skarner are all pretty solid.

Lee Sin us number one (without a doubt) because his ganks are absolutely brutal if you're on the receiving end of a talented Lee Sin's onslaught. He is fairly decent at clearing camps especially if you get some constant life steal in your build.

Dr Mundo is my number two not because of his ganks but because of how fast he clears the jungle and how insanely OP he is late game if you build him as a tank.

Last but not least I think I'd have to rate Nautilus as number three because he is a camp destroyer and his ganks are nigh impossible to escape and his late game tank role is invaluable to say the least.

Skarner is good if you can farm enough from the jungle and ganking to get damage, but Maokai and Nautilus are my favorites because they are more support/tank/junglers who are always useful regardless of gold income.