I've recently started to develop a few domains - just a few at a time. At the moment, one of my sites is doing extremely well, and got over 30 clicks on adsense yesterday - this is a domain that was setup about 3 weeks ago. Having exponential traffic growth due to its topic, and that particular topic's news coverage at the moment, as well as top rankings in MSN Search.
I think the best way to get some cash out of domains that aren't generally great sellers, is to get them online, and get some genuine traffic to them. You can generally cover your domain reg fee in no time for minimal effort.
Take a look at software that can help you do this quickly. I always use wordpress, and i have a series of modifications that I do to ensure better SEO, and thus more hits. Careful advertisement placement can ensure a good return, although I would make sure that you have decent content that isn't duplicated from elsewhere - search engines can penalise you if too much of your content is duplicated from elsewhere...
Jee