There's not really a collector market like Mike said, but where I'm at in Michigan (Detroit area) there is a decent market for trikes. Around here, people will buy them for the Detroit Slow Roll, and there are people who cannot ride a regular bicycle who might be interested.
If it were mine, I would clean it up and put it on CL for around $250 - $300. Keep in mind you may have a tough time selling it this late in the year, and may have to take considerably less if you want to move it before winter. It will sell better in the spring, if you don't mind keeping it til then. The demand for these may vary in your area.
Another tip, get the trike outside in the sunlight and take some decent pictures that aren't blurry. No offense, but blurry pics are about as good as no pics.
Good pics always help items sell faster.
You can list it here on the CABE as well, but you will need to post it in the appropriate forum (Complete Bicycles For Sale) and you must include Pics, Price and Location.
Your best bet though, would be craigslist.