There are some great sales going around the internet right now, with one online store in the second week of their big Summer Sale, and several one-day-only deals on hot indie games.
ImpulseDriven.com is selling Masters of Orion Collection which has Masters of Orion 2 and 3 for $5.99. You can also join the beta of the upcoming indie Space Pirates and Zombies for 25% off at $14.99.
You can get anything at GreenManGaming.com for 20% off if you enter the code Sunny-Saver-20pec. Green Man is also selling several fantasy titles for up to 70% off in their "Dungeons & Discounts" sale. They're also selling Aliens VS Predator for $6.95 right now as well.
Steam is selling the indie game Terraria for half off at $4.99 until tomorrow night, and their Daily Deal today is Beat Hazard at 75% off, for $2.50.
Direct2Drive.com has a sale for Macintosh gamers; the Brothers In Arms Double Time Pack which contains the first two games in that series for $19.95. Again, this is Mac only.
GamersGate.com still has your best chance of finding a good deal at the moment. They're in the second week of a month-long Summer Sale that has close to 400 games on sale, some of them at 90% off. There are some blockbusters like Dragon Age 2 marked down by half, and plenty of indie games at two dollars or less. This cornucopia of fun is our BEST DEAL OF THE DAY.