I like the Delta AmEx a lot for my purposes. I charge ~$1000/month on the card and get anywhere from 1.1 to 1.5 as many miles. Delta offers permanent double miles on a lot of purchases. Off the top of my head:

groceries
gasoline
mobile phone bill
home improvement stores

Unfortunately, it is an AmEx card, so you ocassionally come across a merchant that doesn't accept it. (notably, www.savingsbonds.gov) But for me and my single guy buying habits, that's rare. They also give a 10K bonus with first purchase and they may still give a benchmark bonus in the first year like charge $15K, get a 10K bonus.

As others before me have stated, the *wood AmEx is a good deal as well. I don't have one but for $30/year it's one of the cheaper affinity cards. I don't have one because I don't want to have to deal with the potential credit implications of cancelling my Delta AmEx (I don't think it's advantageous for me to have more than one annual fee affinity card.)

If you want a card that doesn't charge an annual fee, then go for the Hilton HHonors Signature Visa. There is some sort of bonus, plus there's no interest on purchases for the first six months. You don't get a great earning rate at 2 points per dollar, but hey, it's free! plus it can fill the gaps where an AmEx affinity card isn't accepted.