Desura is another digital download site for PC games. It has a client like Steam or Impulse, but it sells games for Windows and Linux systems. Desura also sells a lot of indie games. Moreover, Desura also hosts many mods for games.
I first learned of this site while reading about Xenonauts. Xenonauts creators currently let you prepurchase the game and download it from Desura. Anyway, check out Desura for indie games and Linux games at www.desura.com.