A bunch of smaller sales are taking place on Steam right now.
First, there's the Kalypso Strategy Pack -- purchasable as a bundle or individually -- which ends later today. Given the company in question, we're talking stuff like Tropico, Patrician, and Commandos. Decent games at laughably low prices.
And then there's a weekend sale on the revamped Serious Sam games. Serious Sam HD: The First Encounter is a mere $3.74, while The Second Counter is only $4.99. I bought the eff out of that first one.