I know that you can program for the iPad, but it’s not trivial: you need to sign up as a developer, write code on a Mac computer using Xcode, and go through the app store approval process. How about cutting out all these steps, including the computer, entirely?:
Back when the iPad was announced, my friend Morgan and I talked about a concern some people have with the iPad. Because you can’t program right on the iPad, we run the risk of depriving kids of what many of us consider to be an essential experience: the ability to learn to program “at the keyboard”. Instead, you need another computer, a set of tools, and a complex deployment process to actually get your code running on the device. When Morgan and I were kids, we’d hack in BASIC, and share our creations on cassette, written on paper, and eventually on floppies.
I’ve listed a couple of options (Processing, Scheme), and there are a couple more in the comments. Check out the discussion: O’Reilly Answers – iPad-friendly browser-based programming environments?