Singlefile lets you manage your book collection online: "Singlefile is an easy-to-use web-based service that helps you organize the books you own, the books you are reading, the books you've read and the books you want to read. [...] Singlefile works just like a magazine subscription - you'll pay a yearly flat fee and have the option to renew at the end of each year. Pricing starts at only $19.95 per year."