Steam Summer Sale
 

I know this is a tad late... But from June30th-July10th there will be about 9-12 games being sold at a large discount. Sales are anywhere from 33% off for the newly released games to 75% off for games released within the last year or so.

Just picked up Battlefield Bad Company 2 for $5. It's a great sale for multiplayer games that require Steam/CD-Key, or games that are glitchy/impossible to play if you choose to pirate them (Witcher 2 for example).