I think this seriously depends on what you're trying to do as a movie. I think many games would work beautifully if you did them in the grindhouse style Tarantino's brought back. Low budget, bad dialogue, horrible edits, no CGI. Gimme a Dead Rising or a Fallout movie made in that style, it would be FULLY awesome.
For ones that could be made into a serious movie if done well...
KOTOR - Definitely, but leave Lucas out of the creative process please!
Deus Ex - YES.
Fallout - Seems like no one wants to try and compete with Mad Max or Waterworld. Everything's about the apolalypse lately, but not afterwards. I think we're due for another post-apocalyptic movie soon.
I don't like the idea of RPGs being turned into movies, but they'd work if you picked the right ones. Any involving teenagers saving the world/universe wouldn't work; only epic tales like the Narnia books make that work without being utter cheese. I think Suikoden would work, and you have lots of content to work with. Any others I'd have to think about, but you run into too many cliches with many RPGs, and creating another movie in a fantasy land with magic and dragons after movies like LOTR, Narnia, and Eragon came out... your comeptition is gonna be stiff.