Hilarious. Erik Burnham was just today telling me about this cartoon when we were at FallCon. I come home and find that Blue Spider has linked to the site, which saved me a whole lot of web searching.
So here it is: How Superman Should Have Ended. This requires a DIVX player plugin.
They also have endings for Weird Science, the Matrix, Lord of the Rings, Blair Witch and a bunch of others.