These are the ones I know:
Imagekind. It has a free membership with some storage restriction, paid memberships with more storage. There is a basic price and you add your mark-up price. Never sold anything.
http://adelaidebs.imagekind.com/Artist Rising. It is a spin-off from Art.com (also Allposters.com). If you upload something, it stays in AR until their management decides to upgrade it to Art.com (it seems you have to sell it in AR to begin with, only then they will consider moving it to Art.com). My few sales there were from images I had in Art.com before they created AR. In their forum a lot of people complain they never got a sale in AR. I think they also have a free and a paid membership. They fix the prices, you get a percentage.
http://www.artistrising.com/galleries/madelaidePaitings from Photos. UK-based. The site is actually dead. Their latest news is from March or something. I sent them an email months ago and never got a reply. Also uses mark-up prices.
http://www.paintingsfromphotos.co.uk/photo-gallery.php?photographer=39ArtWanted. I'm new there, only uploaded one image then I found out they have no watermarks. You set your image price (digital file), they set print prices and you set a mark-up.
http://www.ArtWanted.com/?RID=38899&B=text People say good things of Smugmug (requires paid membership to sell). There was a recent thread not recommending RedBubble due to unreported sales, but other than that people had been reporting good results there (but also no watermarks).
Regards,
Adelaide