12.7.12 This page is probably out of date, as I haven’t updated it since the kindle 2. I mean, what I said about .mobi being the same thing as .azw still stands, but I can’t vouch for anything else.
I don’t know how many Kindle owners drop by here, but more should, because reading public domain books has just gotten even easier.
Amazon keeps pretty quiet about what formats the Kindle does and doesn’t support. Here’s what you need to know: the proprietary Amazon format, .azw, is exactly the same thing as a Mobipocket book, (.mobi). The Kindle also natively supports plain text files.
Project Gutenberg has always had all of its books avalable as .txt files, and you can move those straight to your Kindle via USB. Recently, though, they’ve been making their books available in the .mobi and .epub (for Sony Reader) formats, which means that you can get the books with more formatting and, sometimes, illustrations. Mobipocket files, like text files, can be transferred straight to your Kindle with no reformatting.
The Kindle DX, which is available for preorder now, will natively support .pdf documents as well, which means that you will be able to transfer any book from the Internet Archive or Google Books straight to your Kindle without reformatting. I’ve been trying to come up with ways to justify ordering one, but my Kindle is less than a year old, so I don’t think it’s going to happen.
ETA: The Kindle 2–that’s the regular one–now supports pdf natively. I mean, I haven’t tried it out, but that’s what I’m told.