Well, Rotten Tomatoes offers an API, and IMDB offers all their data for download in text files.
Not sure about RT, but IMDB has some fairly strict rules about how their data can be used. http://www.imdb.com/help/show_article?conditions
IANAL but from my reading it sounds like non-commercial use is ok.
If so, is there a legal issue with reusing this data? I actually don't know what the answer is, I'm curious if there is or not.