You know you want World of Goo. Everybody loved it, including us. And you don't want to be one of those video game pirating so and so's responsible for sending a nice indie developer like 2D Boy into the poorhouse. Plus, the soundtrack is free!
The system requirements are low, the game is cheap, and you'll impress your friends with your varied gameplay tastes. What more could you want? A link? Here you go!
World of Goo [Steam]