Afternic.com
Domain name auction site with variety of services like domain news, appraisals, and chat. Recently acquired by Register.com.
Auction2.net
UK based site that mostly caters buying and selling of domains with .co.uk and .com extensions.
Bids4Domains
Allows to buy or sell domains at no extra cost. Free advice available.
BSV-online
BSV aims to be Europe's biggest brokerage company for the trading of domain-names combined with a wide range of supporting services including our unique web-mail system.
eBay.com
World's leading auction site has large selection of domains available.
TopComs
Offering a selection of .com domains for auction, along with general domain information.