Just about every Rockstar game. Alien: Isolation and a ton more Indie games makes up the majority of today's Humble Store sale. A lot of good stuff to check out here.
But Alien: Isolation, 2014's game of the year for me, is $12.49. You can't argue with that. It's good. It's so good. I definitely recommend picking it up if you don't already have a copy. Super Hexagon is 29 cents. Wow.
What else? Man, there's so much. Max Payne 3 is cheap at $4.99, L.A. Noire is $5.99, Gunpoint is $1.99 -- I haven't played that yet, so I think I'm gonna bite on that one.