How can you write a review of Will Smith's I Am Legend without mentioning - even once! - The Omega Man. If it wasn't obvious enough just from the trailers that Legend is a remake a quick IMDB search confirms it. Or maybe they just share the same plot and tagline "The last man on Earth is not alone."

Woops (I didn't check IMDB carefully enough) and both are adaptations of the book "I Am Legend" which was first made into a movie called The Last Man on Earth. [thanks to bobsalive for the correction]