I go to Ursula's every year to get something in where I can spook people.
The amount of masks they have can not be matched, and they have an extensive collections of wig pieces. Bear in mind that they will not let you try on the wigs unless you buy a wrap (for germs).
Ursula is the lady who owns it, and she greets me every time I come to the store. They also have elaborate costumes, but I never had to buy one.
PROS: Wonderful employees, best selection of masks in the city
CONS: Narrow lanes, and hard to reach certain things in store (need assistance)