CS:GO! I already own it on Windows, but can't bring myself to reboot just to play CS:GO when CS 1.6/CZ/S are only an application away. Also looking forward to HL2. I only played the first one of that game, so I'm eager to play the other episodes if/when they're available on Linux. Awesome work Valve!
They aren't in a hurry yet, but Valve needs to bring their most recent games to Linux to make it more relevant.
Though I'm not complaining of course, since we get to have Linux ports of the games, Valve's interest IMO is not to make Linux relevant but to have their games well tested when they introduce the Steam Box. It needs to work 100% when they ship it, and a good way to do that is to drop their ports on us to iron out any rough edges.
But again: I'm not complaining :-P Sometimes ulterior motives can have awesome side effects.
I'll echo what others have said... I want Portal 2, CS:GO, and eventually HL2. I haven't managed to make time to finish Portal 2 yet, and my copy of CS:GO is sitting unused because I usually neglect to reboot to windows when I want to play something.
Now, if only Firaxis gets Civ 5 ported.... (I can dream, right?)
I'm actually against online games being super cheap, because that results in more cheaters. CS:GO is way too cheap IMO (they even lowered the current price below that of CS:S, 11€ vs 15€). Cheaters get banned after a month or so and they just buy a new one. They treat it like a monthly fee.
I own all of the Half-Life 2 series, all of the Left 4 Dead series, all of the Portal series, Team Fortress 2, Counter-Strike: Source, and DOTA2. I have owned the vast majority of them for over two years now but have never gotten around to playing them, except for Team Fortress 2 and a very small bit of Left 4 Dead on Windows 7. I now play Team Fortress 2 exclusively on Linux and have begun playing Counter-Strike: Source on Linux as well and am eagerly awaiting to play all those other Valve titles for the first time ever...on Linux! Make it so, Valve!