I do this a lot. It was only after beating Assassin's Creed that I 'matured' as a gamer, and inherited that completionist attitude which now forced me to beat games, or suffer complete apathy. Fun!
Call of the Cthulhu: Dark Corners of the Earth
Resident Evil 4 (This one is soon to come, I swear it!)
Dead Space (So, so close... O.O)
Final Fantasy X (Currently working on this one)
Final Fantasy XI (I loaned it out to some jackass who let his dog eat it. Worst mistake of my gaming life - one of my favorite games too. I need to Amazon a new one! >.<)
Elder Scrolls: Oblivion (I've never beat the main quest. I 'spose that's just from the Dark Brotherhood being so much better. ^.^)
Resident Evil (I was working on this, until out of the blue FFX decided that it suddenly was 'disc readable' again.)
Edit: I'm so glad I gave away my Pokemon games. I'm sure, that now I would waste away trying to catch them all. O.O