I picked my 12 games:
1. Halo 3
2. Gears of War
3. Grand Theft Auto 4
4. Bioshock
5. Mass Effect
6. Orange Box
7. NHL '08
8. FIFA '08
9. Condemned 2
10. Dead Rising
11. Dark Sector
12. Rainbow Six Las Vegas
Thanks for all of the suggestions, guys.
As for how the deal works, "12 games for $180" was sort of shorthand. It's actually buying a 360 Pro, plus 12 games, for $480. Since the best you'll be able to do on a new Xbox with the 20GB hard drive is $300, I looked at it as 12/$180.
I got this deal on ebay. I'm worried that it's a scam (one of those "too good to be true" things), but I've got the luxury of gambling right now. If it works out, I'll let you know, and if I get scammed, well, then I'm an idiot.