One of the best! ..my opinion at least.

I've seen a couple art sites in my time, but this is one of my favorites. You might already heard of them..

"Thousands of artists from all over the world contribute to the growth and quality of this virtual museum. Our goal is to present visitors the finest gallery of digital artwork on the 'net and to provide artists with a place to share their digital creations, receive feedback, grow their talent, and interact with other artists and visitors." -- digitalart.org

It's like a community there. Real tight. Categories include: Abstract, Fan Art, Photo Manipulations, etc. If you have a taste for the arts, check them out.