I have been looking at Art sites for the past year, trying to find a good market for my work. As a beginner to art marketing it has been quite a steep learning curve. I randomly clicked on the first site I saw that was the top of the google search for "sell your art" - it happened to be a site called "yessy.com".
They offered a 14 day free trial period, so I got my art uploaded. There is no restriction on the number of paintings you can upload so I went ahead. No problem there. I was pleased to see that my work was immediately visible on their network, flashing onto the screen almost immediately after I had uploaded it.
This does wonders for the ego so I was quite encouraged. Then I checked the number of images being hosted on the site - about 300,000! Nothing daunted, I decided I had nothing to lose.
When the 2 -week trial period was over I was offered a year's subscription at about $36. I decided this was reasonable and signed up. Naturally I didn't hear anything in months - no sales, not a peep. Then towards the end of the year, I finally got an email saying that I had a buyer for one of my paintings. You can imagine the thrill that gave me. After a fairly anxious week or so, the sale was confirmed, the painting dispatched and I was $1000 richer.
If you are patient and don't have unrealistic expectations of great sales immediately, you can sell your work, and even get a decent price for it. I have heard that people have good success with Auction sites like E-bay as well. Fanartreview is a great way to get noticed, and a site like wetcanvas is good for networking and becoming known. Eyeoftheart approached me and offered me a free sign up as well.
The more sites you join the better chance you have of selling, although you must be consistent with your pricing - make sure that you put the same prices on your works on each site.
Personally though, I have found that to get real support for your art and to reach a wider audience other than fellow artists who are unlikely to buy your work, you need to get seen on social networking sites like StumbleUpon and Digg. These sites will bring traffic to your art and that is after all the only way to increase your chances of a sale.
A good article on the practical issues involved in selling can be found at this link