• syncing goodreads to librarything: http://www.librarything.com/import/goodreads

selling books

• who'll pay the most for my used books?: http://bookscouter.com/
• various book-buying sites: http://moneysavingmom.com/2012/10/31-ways-to-earn-extra-cash-before-christmas-make-money-selling-your-used-books-day-10.html

recommendations

• http://justtherightbook.com/quiz

used books

• http://www.thriftbooks.com/
• http://www.betterworldbooks.com/

ebooks

• http://www.hathitrust.org/

audio books

• http://ancientfaith.com/podcasts/series/the_chronicles_of_narnia
• http://www.openculture.com/freeaudiobooks

specifically for kindle

• http://www.centslessbooks.com/ -- free books
• http://jungledealsandsteals.com/category/freebies/free-kindle-books/ -- free books, mostly crap
• http://www.wired.com/gadgetlab/2011/01/how-to-strip-drm-from-kindle-e-books-and-others/ -- stripping DRM