I have noticed that some graphics issues might appear when PC games are ported to Xbox. I don't really have a list of games I would like to see ported. Just to name a game off the top of my head, "Blacklight Retribution". The trailer looks pretty cool, and I heard that it is only available for the PC.
I strongly wish for Diablo 3 to be ported over to 360. There were rumors to that effect before the PC launch of a console team being put together by Blizzard, but they are notoriously slow. For those who can't remember, Diablo (1) was on PS2, and I still play it every once in a while. The always online connection would not be a problem, as my Live is always running. I'm sure there would be a downgrade in graphics, and possibly gameplay, but I wouldn't have to worry about buying the game, and having it not work, because of my system.
I'd love to see CS 1.6 & CS:S ported! CS:GO has gotten a lot of praise for it's Xbox version so seeing the older classics on there would be great, especially since they have such a huge following and are extremely active to this day. It'd have to be a direct port and be more so directed to the people who have wanted to play them but don't PC game. Even a lowish end PC could run them but still, PC gaming intimidates a lot of people so it'd be cool to see them receive a lot of new fans, just like games like Doom & Goldeneye have gotten over the past years.