Team Meat have put in a lot of extra characters into their wonderful Super meat Boy, like Tim from Braid or Pink Knight from Castle Crashers for example. The PC-version of Super Meat Boy will feature the Head-crab from Half-Life 2, and today the devs have announced that it will also include Runman (from Runman: Race around the World) and Naija (from Aquaria).
The other bonus characters we already know about from the PC-version are:
Mr Minecraft (Minecraft)
Captain Veridian (VVVVVV)
Josef (Machinarium)
Super Meat Boy is released on Steam on November 31.