If you wondered why the announcement of Company of Heroes 2 was met with excitement, then you can check out the original WWII RTS on Steam with an 80% discount, which is super cheap. Also on offer this weekend on Steam is the recently released Tropico 4 which is free to play this weekend and there's a 66% discount on the game plus all its DLC (apart from the Modern Times expansion).
Publisher 1C is the subject of this weekend's GOG.com discount deal. The King's Bounty, UFO, and Space Ranger franchises are all reduced, along with Star Wolf and Cryostasis. All games are 50% off and cost $4.99. Origin is still making its website unintelligible for finding special offers; looks like they're out of luck here.
If being the Batman is more your style, then Gamersgate has a range of discounts on Batman: Arkham Asylum, Arkham City, and Lego Batman (both on PC and Mac). As always, if you find some cool weekend deals, please post them in the comments as it's much appreciated.