It struck me a while ago when watching an episode of True Blood -- the TV show about vampires -- that we should target people who watch shows like this as candidates for the life extension movement.
In the show (and in some vampire movies and books as well), immortality is generally portrayed in a positive way. Vampires are like an improved version of humans: smarter, faster, stronger, better looking, and most of all, immortal. There's a lot of vampire show/movie fans out there -- more than there are life extensionists, probably. Yet, everyone who is fascinated by vampires is almost definitely fascinated by the concept of living forever. They just might not know that a movement for life extension exists.
In fact, while "life extension" may be the preferable term when dealing with average people, I'd say that "immortality" is the word to use in this case. There's a sort of mystical air to it.
The one thing that these people might not be so interested is science and medicine, so I'd probably avoid going into too much technical detail straight on and just try to make them realize that immortality, with all its romantic notions, is within our reach.