One of the reasons I decided to break down and buy a 360 was an role-playing game called Mass Effect. After 5 playthroughs with 3 different characters, I finally earned all the Achievements (including the 50 points for the downloadable side mission).
I have 2 more games that I think I can get all the Achievements for. (Many games require online play to get all the Achievements. Since I don't play online, I know I can't get those.)