Don't know how we missed discussing this one today. A $5 app for the iPad which will download and read public domain books
to you. No worries about copyright issues.
It's available now. I might pick it up, will post a review if I do (and someone else doesn't beat me to it).
Before you ask, does not say it supports side-loading, only that it can download books from Project Gutenberg.
There's also a review on Gizmodo