Taking Steam recommendations

For those of you who have steam, or any of you who want to go and look up the current sales, I am taking recommendations for purchases. The sales end July 4, so get them in soon!

Guidelines/Info
I play on Mac, so it has be Mac supported.

1. Its a MacBookPro, 2.2Ghz, Intel Core 2 Duo type. Has a GeForce 8600M GT. I take pretty good care of it, but it isn't brand new. Runs Half-Life 2 just fine, but struggles quite heavily with TF2...
2. Check my current library on GB's achievements page
3. I will also be posting both specific questions as well as accepting general recommendations.
4. Don't just link me to GB, Gamespot, MetaCritic, etc reviews, I can read those myself, thanks.
5. I don't want to just hear "This game roxxorz my soxxorz!"
6. If you have Steam, and are incredibly useful in your recommendations, I will gift you a game, limit of $15 USD.

Yep, let me know your thoughts!