I love old movies. I love them so much that I even wrote a book about a 60s movie producer. Some of the best of the old classics have slipped into the public domain, which means they're free. Some of the old PD titles have been put out on DVD over the years, but a great many are in a kind of film limbo, with no easy way to see them if they don't get picked up for DVD distribution.
I'd suggest one nice solution for the iPad. It's called Movie Vault, and it basically lets you stream more than a thousand public domain titles for your viewing enjoyment, either over Wi-Fi or 3G. Now I won't say most of these films are in pristine condition. Quite the contrary. With no studio claiming them, there haven't been any restorations, but there's a lot of gold in those PD hills.
You can search by title, genre, or a director or cast member name. I found a lot of bad films, but I found some great ones, too. For whatever reason, Bela Lugosi was in his share of clunkers. The infamous Plan Nine from Outer Space is one example (well, ... sorta). Lugosi died before the film was made, and director Ed Wood used test footage so that he could put Lugosi in the credits. Another howler is Bela Lugosi meets a Brooklyn Gorilla. It also stars Duke Mitchell and Sammy Petrillo who do an uncanny Martin and Lewis imitation. There are lots of westerns, horror, sci-fi, romance, action and documentary films. One of the gems is The Stranger with Orson Welles, who plays a Nazi in hiding in the United States while being chased by Edward G. Robinson.