My original intention was to inform you that Desktop Dungeons is $7.49 this week on Steam until Friday morning, and that you should play it because it's real good. Hard as hell, but good.
That was until I noticed another game I'd wholly recommend, The Binding of Isaac, is on sale for $0.99 right now. Even with the greatly expanded BoI: Rebirth on the horizon, you'd do well to play the original version. That's countless hours of misery/enjoyment in exchange for a dollar.
Also, Yager's memorable Spec Ops: The Line is vying for our attention with a 75 percent off sale happening now. (80 percent off if you're okay with buying through Green Man Gaming.)