During a limited time period, all ATI customers will be able to get Half-Life 2: Lost Coast and Half-Life 2: Deathmatch free through Steam.
AMD has also announced that customers of the new ATI Radeon HD 2900 XT will recieve a free copy of Team Fortress 2, Portal and Half-Life 2: Episode 2 over Steam when these games become available.
This is an incredible offer.
Read more at http://www.steampowered.com/ati_offer1a/
One more thing: in your face, nvidia users! If you already have these games, be sure to create a new Steam account and claim your prize anyway. Don't let this opportunity slip past you!