Saw this on Destructoid today and thought I'd pass it along.
It's a flash game (Newgrounds) of Super Mario Bros. where you have a choice of playing as either Mario, Simon Belmont, Bill R. (Contra), Samus, Link or Megaman.
Each character is pretty faithful to their respective game's style of movement and attack, although with a few obvious changes to make it possible for them to get past some of SMB's jumps.
Big surprise for me... I'm a lot better as Megaman than any other character.
(I did the regular "warp from 1-2 to 4, and then from 4-2 to 8"... I'm guessing that every level is represented?)