Now this is seriously cool. Let's say you're looking for a book, but it's out of print. Head over to Google Books and do a search for a book. Once you find one you want, copy the URL and take it to PublicDomainReprints.org (if you don't want to use Google Books, there's a search feature here where you can search over 1.7 million titles). Paste the URL into the Reprint Request box, enter your email address, and in a while you'll get a message that your book is available to purchase at Lulu.
I did a search for books containing my family name, and came up with a book of cases argues in the Great Britain Court of Chancery, published in 1820. I requested a reprint, and a few days ago was told that the book was now available in paperback for $14.99. Like I said, seriously cool.
If you're going to use the service, be prepared for a bit of a delay. I had to wait a couple of weeks before my reprint request was fulfilled. Also, because the pages are taken from the scanned documents of Google Books and other online digital archives, the quality of some of the pages may be less than ideal. Still, I think this is a great extension of the Google Books service.