It's a relative unknown, but indie studio Arcen Games is offering their flagship product for 25% off:
AI War: Fleet Command: $14.99 USD
AI War: The Zenith Remnant Expansion (preorder): $7.49
AI War: Fleet Command and its coming expansion are a nice twist on the bog standard RTS, combining grand strategy, tower defense, and RTS elements into a space-based game featuring massive fleets of thousands of ships. It requires cooperation among players rather than contention. It's gotten praise from Tom Chick and the folks at RPS.
It's also coded mainly by one dude who is banking on this game allowing him to quit his day job. He also has a rather enlightened approach to DRM and supporting his customer base. I bought the game full price and don't regret it a bit.
The serial you get with your order will unlock the Steam version as well.
In celebration of the Thanksgiving holiday here in the US, we're having our first multi-product discount sale on our site! Enter code BLLR0018P to get a 25% discount on all games bought directly from Arcen through 11/30/2009. This means that you can pick up AI War: Fleet Command for $14.99 USD, and/or preorder AI War: The Zenith Remnant for $7.49 USD! If you live outside the US, never fear, the discount is equivalent in every currency.