Art Coop saves my ass every time. They are open late and always have what I need. Even though they may not be THE cheapest art store, they are the only art store in town. (And don't even think of calling Michael's Crafts and Poop store an art store.)
Art Coop stocks the basics for any drawing, painting, design, photography class and if they don't carry it, they are usually willing and able to special order what you are looking for.
The staff is friendly (many are artists themselves) and know every product on the shelf. Go on, quiz 'em.