Valve decided that since its revenues are going down, they'd practically give away some games:

Half-Life 2
Half-Life 2: Episode One
Half-Life 2: Episode Two
Half-Life 2: Lost Coast
Portal
Team Fortress 2

$10

TF2 alone is worth that.

http://store.steampowered.com/sub/469/

portal alone is worth 10 bucks.

I'd buy it if I didn't have it already. Definitely worth more than $10.