I'd recommend this art supply store for professional fine artists and graphic artists, but NOT for occasional dabblers/hobbyists/crafters. The supplies they stock are high-quality, professional artist-grade materials, i.e. EXPENSIVE for the most part.
If you are not absolutely sure of what you want and just want to try something out, DON'T come here because you might inadvertently spend a fortune. This is NOT the place to buy student-grade (lower-quality) art supplies.
But if you are a serious artist, and have a good idea of what you need, you will likely find exactly what you are looking for.
If you need advice on materials, the staff is very helpful. Once I brought in a tiny stub of charcoal that was the only one in my art kit that just felt right and made the most beautiful marks. This sweet young lady tested it for me and pronounced it a "6B" grade of charcoal and found some more for me. Now I'm happy because I have a whole stash of 6B charcoal sticks.
Excellent selection of various graphite pencils and charcoals that are priced lower than the hobby/craft stores.
This is the best art supply store in Phoenix, however if you are in the East Valley there are a couple of good stores also.
10-20% Discounts for students, teachers and AZ Artist Guild members.
TIP: Ask to see the kneaded eraser sculptures at the cash register.