Personally, I'm a sucker for video game orchestras, having seen Eminence perform almost every time they've been in Sydney. The recent Distant Worlds concert by the Sydney Symphony at the Opera House made me coo like a dove (say what you will about Final Fantasy games — the music is fantastic), and I have spent hours watching video clips of people performing video game music in their own homes.
Anyway, if I could force an orchestra to perform music from a game, I'd probably make them play Inon Zur's entire back catalogue, which would include music from the Prince of Persia and Dragon Age: Origins.
How about you? If an orchestra was touring with the music of a game, which game would you want it to be?