In case you were interested, I Am Legend has been made into a movie twice before.
First, it was The Last Man on Earth, starring Vincent Price. That one's available on Google Video
for free because it's old enough to be public domain. I've seen it two or three times, and I think it's a pretty good film. It leaves out some of the interesting stuff from the story (like the answer to the question "what if a vampire is jewish?"), but it's still good.
After that, it was made again as The Omega Man, starring Charlton Heston. I haven't seen that one, but it's very different from the book, and I hear it's not very good. Here's a trailer.
I just finished listening to the book on tape of The Picture of Dorian Gray. Great book. It's kind of twilight zoney, and I like that. It's available for free too, also because it's public domain. I found it at Librivox
While I'm plugging free stuff, if you want to read old books for free (rather than listen to them), you can download them for free at Project Gutenberg
More recently, I found out that Baen books has stuff available for free
too! Baen puts out fantasy books, in case you don't know them by name. There aren't a TON of books there, but hey, they're more recent books and they're available legally for free, and that's pretty nice.