(*) Afternic, BuyDomains, Register.com, United Domains, Melbourne IT, Domain Discover, Lease This, DNZoom, Enom, and others.
What other sites are there?
[edited by: Webwork at 5:02 am (utc) on Feb. 27, 2008]
[edit reason] Cleaning up to conform to Charter [/edit]
A note in the WhoIs record, suggesting the domain is "available" can also help.
You may also list domains at a great variety of domain forum or web development forums.
The sad truth is that the vast majority of domains will never find aftermarket buyers unless they are the type of domains that people are already making inquiries about before the domains are ever listed for sale anywhere.
My $.02 is to park them with the best PPC provider that you qualify for that also has a "for sale" option. It's the best of all worlds.
If you track the stats at brokerages you will see that they only move a tiny portion of their inventory and most of those sales are not because they were listed at a brokerage but because the domain was desirable and right priced.
P.S. Don't mind the edit. We really allow very few particulars, as stated in the Charter. (Take a look.)