From posts on other discussion groups I have come to the conclusion that selling prints on the web is very difficult. Having that option as part of an overall site for your regular photography business is the best way to go. One site that you may want to look at is Dave Beckerman Black and White photography. He sells prints of NY on the net but attributes his success to being the number one or two site always on a google search of Black and White photography. I think he states in his journals somewhere it is because he just has a huge number of link backs to his site. it really is not a very well organized site but he sells. He also always has something up on Ebay which allows viewers of his work there to link back to his site.
I have seen articles in some mags such as PDN, Popular photography and Shutterbug that have talked to well known photographers who have said there results selling on the web have been pretty dismal.