Fans are amazing. They should be the ones making the movies, as evidenced by this fan-made trailer for Green Lantern. Even Nathan Fillion thinks this is brilliant.
(If you're on Twitter, follow him at @NathanFillion. Pretend you're friends. That's what I do.)
Also in fan-made corner, there's the Thundercats trailer. It, too, is quite excellently imagined. There are a lot of creative geniuses out there with too much time on their hands. Who would have thought that Troy-meets-Garfield could look so cool?