Spoilers
The movie has an alternate ending included on at least one version of the DVD. The film currently ends with Ash successfully returning to his correct time and laying waste to a Deadite loose in S-Mart. While the scene certainly is funny, action-packed, and kickass (also see Badass), the alternate ending alludes to a fourth film in the series.
In the alternate ending, the wiseman, played by Ian Abercrombie (of Seinfield "fame"), gives Ash a potion, the drinking of which will allow one to sleep without aging. One-hundred years per drop of the potion. So, Ash holes up in a cave, uses his car as a bed, and drinks the potion. Many seasons pass (of course), and Ash awakens and begins to remove rocks from the cave's entrance. He walks outside, and sees not the smoggy blue-gray skies of today, but a yellow sky, and a city in disrepair lies before him, torn apart by some kind of bomb. Ash drank one too many drops, and is now 100 years in the future. The world is now post-apocaltyptic, and, as we know from Ash's earlier flub ups, is still filled with the Deadites.
While the original ending of the film is lackluster (production wise), and the replacement is more exciting to watch, no one can make me not wish for a post-apocalyptic Evil Dead movie. No one.
Now, however, the project seems unlikely ...
Update: May 14, 2002
With the release of the Spiderman movie, Sam Raimi is now a big name among the masses (or, at least, the studios); perhaps Evil Dead 4 is somewhere on the horizon.