Just from reading here and around the web, I see quite a lot of people who use and very much like smugmug. However, it is paid membership only, so you have to be selling a fair enough number to justify the costs. I have no experience with it though; I've explored the same thing (a site to sell images) and haven't found anything that would work for me, mainly b/c I don't sell enough at this point to cover the cost of a pay site.