At the moment? Anything (pre Rage?) by ID and all the HumbleBundle games. On the other hand, all the pieces are in place: OpenGL support is pretty good and lot

At the moment? Anything (pre Rage?) by ID and all the HumbleBundle games. On the other hand, all the pieces are in place: OpenGL support is pretty good and lots of games actually work well enough under wine. That probably means that if they were compiled directly against winelib (as Google did with the Picasa Linux client) they would work just fine. Anything that already runs on OSX is probably an easy port, given some support libraries. That's quite a big chunk of the Steam catalog. I could well imagine that if Valve put some development time into it, they could ship a "PC" set top box based around Steam that would be pretty compelling. One obvious roadblock is that they'd promptly attract a pile of patent lawsuits from Microsoft & Sony as those companies tried to protect their existing platforms, but I'd love to see them do it.