The Capital One Venture card is one of the best cards out there if you want to earn airline miles. You get two points per dollar, and can then redeem them for flights (as well as other things) at the rate of 1 cent/point. I.e. a $500.00 plane ticket costs you 50,000 points. This is different from most other airline credit cards, whose award-miles-per-flight rates vary wildly depending on demand. For example, even though the jetBlue credit card gives you 1 point/dollar, it turns out that when you redeem points for some flights, each point can be worth as little as 0.75 cents/point.

According to NerdWallet, the Southwest Airlines card is really good: 25000 miles on signup, 1 mile per dollar, double that on Southwest expenditures, and 3000 mile annual bonus. There is a $69 dollar annual fee, and Southwest tends to be relatively light on the perks that you get for flying with them a lot.