Karina over at Spout pointed me to this great list of web apps for filmmakers with iPhones. (Note that these are web apps, not iPhone apps you download.) Paul Harrill at Self-Reliant Film put it together.
IMDb iPhone Client
Web interface with support for looking up actors, characters and movies. The client also helps you find trailers that are suitable for viewing on the iPhone and view additional information such as: Goofs, Soundtracks, Trivia, Quotes, and Crazy Credits.