There are a lot of places and ways to sell on line. Most of the ones that charge you do not necessarily get you views or sales.
As a professional artist I strongly recommend that you start a blog. You can add paypal buttons and sell directly off your blog over time as your collectors grow. 90% of my sales are off my blog. You need to post at least weekly to keep up the interest and your rankings on search.
Suggestions for an art blog:
KEEP IS BUSINESS- collectors do not want to know about the shoes you bought or what you had for dinner. Focus on your art and inspiration.
Be sure you can be contacted- have a working email address.
Be sure you MARK YOUR IMAGES with copyright and your name- ( If either of the Orphan Works bills pass you will need to protect your work even more diligently when using the internet.)
Keep image sizes smaller – though this will not prevent theft will help. General rule of thumb- 72 dpi no larger than 4” in largest side.
Also add to your blog an automated email list for folks to get email previews of each new work of art as it is listed complete with paypal button. This can be done for free using google groups and blogger.
Keep your prices consistent or your clients will not consider your work an investment. Most artists charge by size.
Be patient and keep working. It takes time to build your client base but if you build it they will come.
As for FREE sites for selling art in addition to your blog
Artbyus.com Free for basic listing.
I have found that pay for sites very rarely bring sales.
In regards to Ebay- it is expensive and time consuming to build up a following. Once you have built up a following you must always list or lose the following.
Those who are successful work hard and pay lots of fees.