All you really need is art.... heh, used to be a great commercial in the US.
Anyway, here are some art sites that I recommend buying art from:
http://www.artbank.com I haven't signed up to sell my paintings here, so I can't vouch for anything, but I am in the process, so I'll tell you how it goes, looks like a nice site.
For the local artists (AU) I recommend the Art Shed. They have good canvases at great prices. The Oils are basic but cheap and the larger tubes... I don't recommend the paintbrushes as they tend to be on the cheap side. I also purchased a nice French easel. Nicely done, I would perfer a stained version, but the natural one is fine. I haven't really tried anything else there. Overall good store.