You can post them for sale on sites like this, ebay, post a message on the domain that it is for sale or you can try selling it from your home.
We had pretty good luck last Summer with our Domain Garage Sale. We put up signs in our neighborhood that pointed to our house, and people that drove by would see the signs that we were selling domains and they stopped by.
We also took out an ad in a local newspaper under the "Yard sale / Garage sale" section. I think it cost us $17 dollars for the Saturday and Sunday papers.
What we did was take things from our house and then put a sign on each one that had the domain name. Like a hockey stick had a sign with our Hocky.us domain and an asking price. A frying pan had a sign selling SpamCracker.com, and so on. If we didn't have something good to put a domain name on, we just got a photo or drew a picture the best we could. I remember taking some gold paint and making a credit card picture for GoldCard.ws and everyone thought it looked pretty good...! (It didn't sell, but I think I was asking too much...!)
One suggestion if you try this: Don't put any domains down at the end of the driveway just to make sure people see them. One of our domains got stolen and we just stopped another person that thought it was a freebie. Keep them close to the house!