I'd recommend the Company of Heroes since for $12 you get something I had to special order from the UK for $35, last year. Company of Heroes is a RTS with many unique factions in it, and an amazing set of single player campaigns through at least the first expansion. The third expansion is mostly cosmetic, except for the Tiger campaign which is a bit of fun...but then World of Tanks came out.
Audiosurf is pretty good too, and worth $3 just to see how it interprets music into roller coaster tracks. Beat Hazard is better if you actually want to shoot something while listening to music, though the music interpretation is a bit more in the visual display of the game.
Counterstrike:Source is ok once in a while. If TF2 had terrorist-bombing game mode, I don't think I'd ever load up CS:S.
Street Fighter in High Def looks like the real winner today!