There are many ways to shop for books on the internet (and in "real life")

 Many shoppers use a few large meta book search engines when shopping or browsing for books.  There are more large book sellers that also sell books online.  Here are just a few of them:

*  Better World Books

*  Strand

*  Powell's Books

*  ABAA

*  ILAB

*  Target

*  Barnes & Noble

*  Walmart

*  Blackwell's

*  Used Book Search.co.uk

*  ebay

These are some of the larger sellers of new and used books on the internet; other shopping options include virtual book fairs, online auctions, publishers and book search agencies (in addition to brick-and-mortar stores, most of which have a website.)   

*I don't receive a commission from any business..