Goodreads - See what your friends are reading.
eBay - Buy and sell electronics, cars, fashion apparel, collectibles, sporting goods, digital cameras, baby items, coupons, and everything else on eBay, the world's online marketplace
LibraryThing - A home for your books.
Amazon - Online shopping from the earth's biggest selection of books, magazines, music, DVDs, videos, electronics, computers, software, apparel & accessories, shoes, jewelry, tools & hardware, housewares, furniture, sporting goods, beauty & much more
MyAnimeList - Start cataloging anime you've watched or manga you've read.
Bookfinder - Find nearly any book: new, used, rare and textbooks.