Strategy fans might want to take a look at the new Humble Monthly, as it includes Hearts of Iron IV.
Hearts of Iron IV is the highly rated World War II strategy game from Paradox Development Studio, one a few friends of mine have spent a great many hours in. For $12, it's worth it for that alone, since that's actually the lowest price I've seen it (Steam's lowest for it in comparison was $15.99 during a sale).
It also includes two other games: Blackwake, a multiplayer naval FPS whose developer has said they will attempt a Linux version closer to release and it also has Portal Knights, which is not on Linux and no hints of it coming.
As usual, subscribing to it also gives you access to the Humble Trove, which has quite a number of Linux games (over 30 last I checked) and Humble are gradually adding more indie games and unique games as time goes on.
Check out the Humble Monthly if you're interested.