I love Costco for all of it's quantity glory. They have almost anything you need at great prices as long as you need a ton of it.
And the pizza, hot dogs, smoothies, churros, and ice cream that are super cheap, how can one go wrong?
Don't forget the cheap gas, it's usually a few cents cheaper per gallon than other places and there is rarely a wait.
My one knock on Costco is that I refer to it as the place where people check their humanity, common sense and manners at the door. Some people just have no sense of the other people around them and you will get people who stop right in front of you, stand or leave a cart right in the middle of an isle, or literally run in to you with a cart.