Amazon's probably your first, best stop, with Marvel Ultimate Alliance 2 for $30, Metal Gear Solid 4 for $15 and more on the way. Amazon's also offering $20 in PSN credit with the purchase of qualifying PS3 games. Gamestop's putting out a good spread too, with $20 off LittleBigPlanet and $25 gift cards on plenty of games including Tony Hawk Ride and DJ Hero. The Guitar Hero Store has slashed prices on a ton of bundles. Quite a few retailers have discounts you can use for video games (or anything else you're buying) through Google Checkout as well.
Spot any good sales? Let us know in the comments.
[Update 1: GamersGate has posted its deals.]