I'd suggest you start by reading this thread:
How to Market Domain Names and Connect with Buyers [webmasterworld.com]
From this forum's library. (See link at upper left of Domain Forum's homepage.)
Check:
Home > Buy > Computers & Networking > Other Hardware & Services > Domain Names
Or just search for "domain name" then click up to the top of the category after you find one.
I poke around there from time to time. To cut through all the junk, use the box on the left side of the page and select the check box for "Number of bids" and set it to "1" in the lefthand field, (which means one or more bids --- anything decent listed for more than a couple hours will get a bid). You'll see how much the names are fetching. There's a 3-letter .COM name with 21 bids going for over $20,000 right now, a common first name ".COM" for $28,000, and (lots of name going for $10-$20 bucks).
BEWARE OF TRICKSTERS if you are considering buying there.. Like the names that look like they contain the letter "O" but really use the number "0" (zero)... People advertising "6,000 backlinks" and Google PR6 and willing to sell for $10.00 --- they are using redirects and just plain B.S.
If you have decent stuff and write an honest listing, you may be able to sell off some names.