It's a shame one of the other reviewers had a poor experience at Top Notch, but I've been shopping there fairly frequently in the past year and I've always had a pleasant experience.
I'll admit that I don't shop around too much for art supply prices, but I can say with confidence that the majority (if not all) of their items are more affordable than what you'd find at a university book store, especially considering that they have a huge sale at the beginning of each semester as well as a year-round student discount. In my experience, they have a wider variety of products as well, at varying price points, just in case you can't afford top of the line, professional quality supplies.
I've always been able to find everything I need there and the staff is friendly and helpful. The fact that it is within walking distance from my campus is a HUGE plus.