In the meantime, you might find
Project Gutenberg, and
Manybooks of interest. They have more or less the same set of books at both, but Manybooks serves them up to order in a bunch of formats, which means you'll do less conversion to get them on your Palm. There are other sites, of course, but those two are a good place to start.
If your son likes Sci-Fi, I'd also recommend Baen Publishing's
Webscriptions service, it's not a free site, but the stuff is recent releases, the prices are quite reasonable, and there's no DRM on any of it, and they do offer a couple of formats in their standard set that will run on a Palm without any conversion, which is nice.