Below are a few domain sales sites worthy of attention. PayPal is usually the system of choice but most sites will use Escrow.com as well.

BuyDomains.com
The 800-pound gorilla of all domain sales sites. The prices are not cheap, but BD has one of the largest domain portfolios on the Internet with premium names galore.

DotComAgency.com
Not as large as BuyDomains.com, but it still offers many premium names at premium prices. In order to find out what they want for a name, you have to request a price quote.

GiantNames.com
Over one hundred premium and cheap domains for sale. Most of the names show pricing info.

TLDN.com
Offers a large number of high quality domain names starting at just $8.50.

Internet Burst
Supplier of high quality search engine keyword domains.

100DollarDomains.com
A standing portfolio of over 1400 names for sale, all affordably priced at $100 each.

Awesome.biz
Offers a huge portfolio of .info domains. Definitely a nice use of a .biz domain.

PerfectName.com
Focuses primarily on premium domain names.

ReadyDomains.com
Your new domain is ready at ReadyDomains.com! Shop for top-level domain names at affordable prices.