DF and I love Costco. IMO, it is better than Sam's (and I love what Laurie said about the CEO). I really like to get things like toilet paper, paper towels, detergent, dog treats, etc. Things that I don't want to run out and buy all the time but need frequent replacing. They also have great prices on books but I have noticed their CD proces are high. One amazing deal is Sabra hummus (with the red top...sooo good). A small thing of it in the grocery store is around $4 or more. It maybe has 8 servings. The huge tub at Costco is $5.69 and it probably has about 30 servings! There are other things like that as well. Their food, fruits, and vegetables are always good but it can be difficult to use it up before it goes bad.
They also have an AmEx card that you can get. They give you a $25 refund when you join and you get 1% cash back on all purchases, 2% on food and travel, etc. (I think those are the percentages). It's a really good deal and they are giving 0% interest until November (although we don't keep a balance, just use it for the cash back).
Okay, I need to stop. I sound like I work for Costco!