MyMovies is widely used and stores everything in a SQL db but also creates xml files. There is an MCML program called VideoBrowser that reads these xml files in a nice interface and uses MyMovies purely as a backend, kinda like what your app would be doing.
There is another app by somebody named Salami (
http://thegreenbutton.com/forums/thread/250545.aspx) that scrapes data from imdb and stores in the same xml format as MyMovies, for use by VideoBrowser. I would suggest this as it downloads the artwork as well and creates nice clean xml files without the need for another huge app and SQL backend like MyMovies.