What are the best art supply stores in the San Francisco Bay Area?

http://archsupplies.com in potrero hill

I went to Flax on Market per 's suggestion, and it was wonderful.  It's convenient (right on Market and Valencia, with its own parking lot on McCoppin) and has an incredible collection of paints, easels, canvas, notebooks.  They also had a considerable children's arts and crafts section.  Most of this is on par with or better than the typical art supply store.  Their prices were also pretty competitive.  What I was most impressed by was their collection of papers; they have more varieties than I've seen in a really really long time.