Aside from public domain books and creative commons stuff, a fair ammount of authors self-publish their books for free on Feedbooks. Some of them are very popular:
http://www.feedbooks.com/userbooks/downloads
You'll find some of those in the guide too, but I'll improve this part of the guide in the future.
I'm planning to use some of the new Kindle 2 features as soon as I figure them out, such as the new way to browse, or the new TOC system for newspapers (I would use this on our RSS feeds). The good thing about our system is that I can update ALL the books. This way, every book on Feedbooks will get these upgrades.
I've also boosted our metadata, but the information page of the book doesn't show the description on the Kindle 2.