The Smash Bros series, for one. You've got all the mainstay Nintendo characters in there. The Soul Calibur 2, 3, and 4 have cameos from characters from other [url=http://www.buissy.com/collaboration-software]Collaboration [/url] series (character depends on what system you get the game for... the GameCube version of 2 has Link... The PS2 version has Hieihachi).