WebSiteBroker.com is a service that specializes in listing complete websites for sale, and each website has a complete overview along with statistics and other information making it easier to make an educated decision. The site also has a tab to switch from websites for sale to domain-only listings.
Listings can be sorted by price, daily traffic and a variety of other criteria. The site also offers a guide to valuing websites, along with a resources section that provides links to many useful resources related to domain names.