Wiggitty,
The second version in this set has a different ending. I know of some other stuff, but I don't want to be spoiler man.

I DO know that the actual director's cut was an hour longer than the theatrical release. It also had more scenes that were directly copied form The Omega Man, such as the Mustang being driven thru the showroom window. Hopefully, they will release that one eventually.
Preporduction on I AM LEGEND II has begun. At this point, Will is not attached to the project. Since he be dead, I guess it would be a prequel. That would rock.