Heres some good games you can get cheap off steam!

http://store.steampowered.com/app/2310/

http://store.steampowered.com/app/10/

http://store.steampowered.com/app/70/

http://store.steampowered.com/app/380/ (comes with source sdk!)

http://store.steampowered.com/app/280/

http://store.steampowered.com/app/360/