Only game I want to go on sale is Don't Starve. I have everything else I could want to play.
Highly recommend getting it now, it is 20% and you get a second copy as a gift. It has quite difficult gameplay to begin with but you progress slowly to understanding mechanics and what to build when. It is progressing quite well for its beta stage and updates are quite steady with a new one that just came in yesterday.
I'd also like to know how Natural Selection 2 is, had my eye on it during development and would be keen to hear some feedback.