Plex Media Center
I would STRONGLY recommend the Plex App with Plex Media Server.
http://itunes.apple.com/gb/app/plex/id383457673?mt=8
http://www.plexapp.com/getplex/
The Media Server will run on your Mac/Linux/Windows machine and manage all your media beautifully. It will automatically download covers, synopsis, genre, actor/director, rating etc.
But most importantly, it will act as a hub to distribute your movies/tv shows/music to a range of client devices (including your iPad).
Just download the Plex App (link above), it's only £3. The Media Server is free.
The best part is that it works on both your internal network, and over the internet! If you have a decent enough upload bandwidth you can stream 720p (and even 1080p) over the net without a hiccup! Setup & Config is an absolute breaze too. So I have access to my library of over 800 films (all HD) from anywhere in the world.
I have my Plex Media Server sending content to my iPad, my wife's iPad, my living room AppleTV (this has to be jailbroken to install Plex client as there is no official App Store for AppleTV yet). And then you can securely share your library with others too. So my brother from his home also has access, and well as my in-laws home. It's fantastic.
The only thing I keep on my iPad are Apps and a selection of Photos. If I'm gonna be travelling on a long flight, then I'll store a couple of movies on there. Otherwise, movies are always dished out via Plex.