Just a quick reply here with a list of 360 games I've yet to finish, as I'm on my way out the door right now. When I get home I'm looking forward to perusing the other lists and seeing if I can't persuade anyone to finish a particular game of theirs.
Oblivion - Love the game, and I've put easily 100+ hours into it. I'm on my second character now, for some reason last year I was forced to make a new XBL handle and as a result had to start over most of my games. I've actually gotten back into it recently, gotten up to about where I left off with my old character. Planning on finishing the main questline sometime soon.
Fallout 3 - Beat the main questline and a good chunk of sidequests, just need to work my way through Broken Steel. Again, love this game.
Assassin's Creed - Borrowed it from a friend ages ago, never really gave it enough of a chance. I want to beat it so I can play the apparently better sequel.
Dragon Age - I'd say I'm about halfway through. I do like this one, but I find it hard to really dedicate the hours that it deserves for some reason.
Mass Effect - Same deal as with DA:O, except I'm right at the end of this one. Looking forward to finishing it so I can get into ME2.
Final Fantasy XIII - I bought this game the first day it was out, can't even remember the last game I did that for. I was fully addicted to it up until I reached Gran Pulse, then for some reason I couldn't bring myself to trudge on. I assume I'll beat it someday - I don't think I've ever beaten a FF game my first playthrough.
Prototype - The idea of this game is awesome, and all the powers you get are very fun. However, the missions are kinda lacking in my opinion, and I'm stuck at about 3/4 of the way through.
Burnout Paradise - I have no idea how far I actually am into this game. It's great fun to throw on every once in a while, but as with most racing games, I've never really sat down and put my mind to playing through it. Maybe someday.