Eyestorm
I found this site the other day, their index of artists is pretty extensive and definitly worth checking out.
"Eyestorm is the leading online gallery of limited edition contemporary art. Founded in 1999, Eyestorm came under new management in 2006 and has refined its operations to make buying the finest contemporary art easier and more enjoyable than ever before. Come and visit us at our new Bankside gallery next door to Tate Modern in London"