beautifull katamari 15/40
To be fair, Katamari's achievements are ridiculous. You can't get them all from playing the regular retail game--you have to buy ALL the DLC just to earn the last few.
I've got 30/40 on Katamari, which is all the ones you can get through regular gameplay. The online play kinda sucks, so I don't have those, nor the ones you need to pay for, because that's stupid.
My highest is 41/42 on Transformers: The Game. Everything except 100% completion, because I'll be damned if I'm going to hunt down all those Energon cubes.
Rock Band's coming along. I've got 17/50, but I'm starting to finish off towns in World Tour, so that'll keep growing. Only thing is, I don't see ever playing drums on anything but Easy, and I think I'm hitting a wall halfway through solo guitar on Hard, so I'll only get so far.
Halo 3 I've got 15 of 49. I need to finish the single-player game.
My other games I haven't played enough to earn much yet (Simpsons, GTA4, GRAW, Madden 07, Viva Pinata) or haven't even unshrinkwrapped yet (Guitar Hero III, XBLA Unplugged) or are designed to be just plain impossible to get any achievements at all (Earth Defense Force 2017)