Steam has a fantastic reputation when it comes to supporting indie games, and one of the newest titles on offer through the online store is the unique puzzler Lucid, which came out a few days ago and is only 3.99 right now. The game will go back to 4.99 once the launch week special ends, but for now its 20% off.
I enjoy puzzle games, they're fun and I can pick them up and put them down when I want without worrying about forgetting controls, plot points or what quest I am currently on. Lucid also features an interesting gameplay mechanic that I would expect to see on a mobile device, not the PC, where you "paint" a line connecting the gems to be removed from the level. The interesting part about this is that the line must remain unbroken. The music is also incredibly chill, and relaxing music can never be a bad thing. Well unless you want to be angry, or are secretly the Hulk.