Lots of PS1 era games (and even PS2) deserve to have their graphics touched up and re-released for Xbox 360 and PS3.
And Im not really talking about 2D games because then you get into the whole discussion of if 2D versus 3D. Im mostly talking about the games that came out for PS1 like the original Silent Hill and the Resident Evil games. When they originaly made those games they were limited by the hadware of the time, but now they are free to make the games as they were intended. Even if it was just better looking character models and some added facial animations would make a huge difference.
And Im all for seeing the new games in these series, but I would like to play through the old ones again, with some nicer looking graphics.
They could release these as downloadable content or they could release all the games in a series as a boxset. These games have lots of fans and Im sure any fan would like to see these games touched up.

Silent Hill
Resident Evil 2, 3
Final Fantasy 7,8,9
Dino Crisis 1,2
Fear Effect

what else?