There are actually several trans films, but I will say that crossdressers do form part of what is considered transgendered in the broad sense, because they do step outside conventional gender boundaries.
The film "Second Serve" with Vanessa Redgrave is a bio-pic of Renee Richards, a tennis player and former naval doctor. The main character is played by a woman (cheating)
"I Want What I Want" is a film based very loosely on a British novel, and once again cheats, starring Anne Heywood.
"Different for Girls" is one of my favourites, and is available on youtube. Another Brit film, the last to feature Ian Dury, and the main character Kim is actually played rather well by a man.