I've been meaning to share my new favorite on-line bookseller.
I got to them through
www.iGive.com where I went and typed in a search for used books.
BetterWorldBooks.com won me over first-off by the fact that on every page for a book there's a link for "search for this book in your local library." How cool is that? They run book drives for schools and libraries, and a portion of every purchase goes toward funding literacy programs worldwide.
They sell only used books (or remaindered, which isn't quite as awesome as used, but sometimes that's all that's available, and they point out that they're diverting these from landfills), and show you amazon's price for comparison. When available, they link to Google-preview.
Oh, and shipping is free inside the US ($3.97 internationally), and when you check out you can purchase optional carbon-offsets for your shipping.
I think they're pretty awesome, and so I wanted to share.