well, I'd think that Half-Life 2 is next up. Just like they did with CS 1.6 and HL 1.
Also another multi-platform game is currently trying to hit Steam: Vendetta Online, would be nice if some people could upvote it. -> http://steamcommunity.com/sharedfile.../?id=124255217
so? Adobe Flash works under Linux since ages.about csgo, it uses flash to render the hud, so i dont know if it will be ported at all