To celebrate Q Games' 10th Anniversary, the team behind the PixelJunk series of games are hosting a monster sale on the PlayStation Network.  You can snag PixelJunk Racers, PixelJunk Monsters, PixelJunk Shooter, and PixelJunk Eden for just $1 each.  More recent titles like PixelJunk Shooter 2 and PixelJunk SideScroller are also half off.

Pixel Junk Monsters features a two player Co-Op mode in which players join forces to defend themselves from a constant onslaught of enemies.