This department store is a good bet for many purchases you might need to make while in Cancun. We…read morecame here a few times looking for stuff we'd forgot to pack or needed (electronics, clothing, make-up, and more).
It is located in the La Isla Shopping Village in the Zona Hotelera, so it's convenient for most tourists.
In addition to all the stuff you'd expect to find in a department store, they have a "Tax Free" kiosk that will help you file for the return of any Mexican taxes you pay on goods you've bought while in Cancun (and not just stuff you bought in Liverpool, but anywhere--as long as you have the receipt, credit card, passport and your flight info with you). This makes it worth its weight in gold (or at least, in Pesos...). The attendant, Martin, was very helpful and we visited him so many times that got to be on a first-name basis with him (if you go there, say "Hi!" from me).