I love Costco - you do have to watch prices, tho, because you're not necessarily getting a 'bargain' on all their items - you have to do the math, break the cost of say, a case of something and then compare it to what you can find in the supermarkets - for instance, I see folks all the time with those huge packs of toilet tissue and paper towels, but I can find better bargains in the local supers when they're on sale. However, their prices on flour, sugar, etc. are fantastic. (if you should find yourself needing 25 pounds of flour!
Other things I find myself buying just because you can't find them anywhere else; they have a frozen 'lime and cilantro shrimp' that is to die for! We just nuke a few and throw them on a salad, and the taste is awesome!
And i also agree that their 'Kirkland' brand is pretty high quality, too - saw a bottle of Kirkland Shiraz, I think 2000, for $49!!!!!