www.bonanzle.com is free to list and have a store (called a booth there) plus low commission on what sells.
It is an online selling community with a lot of focus on social interaction via forums, selling games etc.
It is really simple to run a store there which is a big advantage




www.ecrater.com is totally FREE (free store, free listing, no sales commission) and was recently announced as one of Google's partner sites so items rank well

there are others, but it depends on what you are selling...the 2 above are for both old and new stuff

eBay still gets the most traffic, but you do have to be prepared to part with a chunk of your profit with all their fees