We are thrilled with our Costco/American Express Card, which we have had for several years now. You do have to be an "execuitve member" of Costco to get it. That particular membership cost about $100 per year, but for us, it is worth it. We get our business checks through Costco for a considerably lower charge than the bank, and we also use their credit card processing company for my husband's business.
This American Express has no yearly fee. You get a rebate for every dollar you charge. This annual rebate has to be redeemed at Costco, but you do not have to use it for purchases. You can simply get cash. The service is great. When someone got my husband's number and charged some purchases, American Express called us and told us there were suspicious charges that did not fit our "purchasing history." When we verified we had not made those charges, they acted immediately.
We put just about every purchase on this card in order to get the rebate. We do pay the entire amount off each month, so we never have a finance charge. Just like any other credit card, you do have to be careful with this.