I have just discovered RedBubble an awesome site for displaying and selling your artwork (whether images, writing, T-shirts or otherwise)... and developed in Ruby-on-Rails too.
You can upload your art and offer it for sale in a variety of formats - they provide widgets for helping sell your stuff (eg the portfolio below). You just specify the markup you want and they take care of the shipping and payment - sending you your cut via checque or paypal. It also has groups a-la flickr - where you can join your art with other similar art, take part in challenges etc.
Here's my portfolio as an example of what they can do for you.