Fiddle is extremely squishy and does not deal with counter-jungling very well.

idk but try ap shaco

You have to be very skilled but there are 3 APs whose jungle and ganks are phenominal. Sona can slow, stun, long range poke. Soraka can tower dive at lvl 4 spamming starfall with spell vamp killing everything. Heimerdinger can out farm nunu in the jungle and when he sets up ganks in pushed lanes they will die end of story.

nunu would be fun and easy.
he is my fav jungling AP champ.

I'm surprised no one has mentioned jungle Eve. She doesn't rely on blue, has good ganks, even better ones post-6, can bypass wards, has decent counter-jungle and high mobility. Her clear times are decent and she scales well into late game, and she has enormous potential to snowball. The only thing against her is her relative squishiness.

Cho'gath and Nunu are my personal favorites.

Oops, something else I didn't notice and need to address. Shen is not slow. He's not the fastest jungler, but he's definitely not the slowest, and in addition to clearing in a reasonable timeframe, he also does so with alot of health left, allowing him to gank several times before his first back. Also, he's not AP. He's a tank, with an emphasis on AD(especially attack speed) when he chooses to build offensively.

Hehe. I know people will get mad at me for saying this, but I've tried it many times and it works well. AP Karma jungling. The clear time is amazing, the sustain is great, and without an ult, she's pretty easy to do it with. The problem is really that the ganks are horrible. She has a slow. That's it. But it works, and its fun to do for laughs.