I'm another big fan of the Costco AMEX card and a few of the others. I used the United Mileage Plus Visa for years but found it to hard to get the seats we needed so I started using the Costco card and another BofA cash reward card. We easily get over $1,000 cash back every year. That's enough for 2 round trip tickets on any airline to almost anywhere in the US including Hawaii. (at least for us)
The secret is to charge EVERYTHING, and I mean everything. Many people would be surprised at just how many of there monthly bills can be put on a credit card. This includes a lot of the expensive bills like car insurance, DMV fee's, etc.
Of course you have to be disciplined enough to pay it off in full each month. I haven't paid a cent in finance charges in years.