Did anybody mention the Prince of Persia?
That'd be awesome.
They should also add Sonic and Shadow from the Sonic series. Oh and defenately Knuckles. In fact, scrap sonic and shadow. Just Knuckles.... yeah... that'd be cool.

Here's some more characters for you to add

-Himura Kenshin

-Sanosuke

-Saito

-Aoshi Shinomori


Those would all be awesome charachters to use. Unfortunately I'm afraid that all of them except sano would be too much alike. Sano could be a fist fighter and pull out the zanbato but Himura, Saito, and Aoshi are all just swordfighters.