One of my favorite film festivals is Sci-Fi London, which will be coming around again from April 28th to May 3rd, 2010. If you build your own Science Fiction or Fantasy, be it live action or animated, they would like to see your film and consider including it in their festival. Submissions are now open at their web site; if you want to get an idea of the kinds of things they will accept, check their TV segment and watch some videos.
Likewise, on this side of the pond, the Boston Science Fiction Film Festival coming up February 5 – 15th, 2010, is also looking for submissions. In fact, they are almost done, but you still have time to get your film in (just) with the regular deadline on November 30, and the late deadline on December 15.