I don't know how long this alternate ending to I Am Legend will last but if you get a chance, you should watch it if you've seen the movie. This ending is IMHO far superior to the abrupt version in the theatrical release, and fits in better with something that happens in the film about midway through.
I didn't post this up earlier because it was only available on YouTube, and videos of this sort get yanked pretty quickly and them I'm left with a useless post. :-)
GameTrailers.com has a version which I've embedded below, which will hopefully hang around a bit longer.
At one point in the movie when Will Smith's character took the lead zombie's mate away from them, the zombie reacted with extreme rage, indicating that there was some vestige of humanity left in them. But throughout the rest of the movie we never saw any more hint of that, which felt "unfinished" to me.
Well this clip addresses that very nicely, plus doesn't have that nihilistic ending with Will Smith dying. I don't know why they didn't go with this ending... maybe they thought it was too cliched for Will Smith to survive - but in this case I think it would only have made the film better.