If you are feeling ambitious, you can link each of your domain names to its matching “buy it now” purchase page at one of the marketplaces. Another more sophisticated option would be to “park” your domain with one of the leading domain parking companies, such as DomainSponsor or SmartName and enable their built-in “for sale” message and contact mechanisms.
Here's a test I have in process. I bought an old $5 closeout domain from Godaddy TDname expired auction. I put a quick minisite up and linked to it with a crazy anchor text phrase. The domain is ranking for that crazy term now. It's gone through one pagerank update and I'm waiting for a second to come. Then I'll redirect the domain to another minisite. I suspect the second site won't rank for the anhor text, but we'll see.
1) pending delete auctions. These are domains that were not renewed and are going through a pretty complicated drop process. You can backorder these names at the auction venues and then each attempts to "catch" the dropping domain. If one is successful you win the domain at $59 if you're the only one to backorder the name. If more than one person backordered the domain a 3 day private auction is held. Once the domain goes through the drop process, the back links have pretty much zero SEO benifit to the new domain owner.
There’s an important distinction to make here between domain flipping and website flipping. The latter mainly refers to buying and selling full websites. By full websites, I mean websites that actually have content and more often than not have traffic and revenue. When buying and selling websites, the domain name matters less as the main value there is the content, traffic, revenue, history/reputation, sustainability and growth opportunities. The same can’t be said for domain names where you’re just selling “the name” and hence it’s all that really matters.