Super Mario Crossover - Playable Game
 

Description: One of the best Mario games ever! You can also choose any other classic Nintendo character to play with in this Mario based platform.
Instructions: Use arrow keys to move.
Z,X - action buttons.

The flash game--which can be played for free at Played Online--might as well be called Crisis On Infinite NESes, as it recreates the entirety of "Super Mario Bros.," but with the added bonus that at the beginning of every stage, you can choose to play as Samus Aran from "Metroid," Link from "The Legend of Zelda," Mega Man, Simon Belmont from "Castlevania", Bill Rizer from "Contra," and, of course, Mario.

Each character works exactly like they do in their own game--Link has his sword and boomerang, Simon throws axes, Bill has a friggin' machinegun, and so on--and as an added bonus, each one comes with their own background music.

Thought some of you might be interested

This is pretty sweet... need to get it into the arcade :D

agreed, this game is sick!

here's the newground link:
it says you can use the game on whatever site you want as long as you link to the creators homepage

For all you fans of the original NES, here is a site that has almost all the games that you can play online for free.

I also like nintendo8.com, which is java based nintendo games.