I'd like to introduce my personal favorite: the American Express Starwood Preferred Guest card. I use this for the majority of my purchases. The points from card are worth much more than your average card.
You can use the points at any of the Starwood Hotels (W, Westin, Sheraton, Four Points, etc.) Though it varies, I sometimes can find rates to stay in a $250/night room for 3000 points! In this case, the points are worth 8x the points on your normal card. For the sake of example, the same 3000 CapitalOne points will give you $30 off a flight, and doing the math says you'd need 25,000 CapitalOne points to get the equivalent $250 savings.
I don't like to waste SPG points on airline points. If you choose to, you'll get a 25% bonus when you transfer these points to airline points. Most other cards you only get 1 to 1. Each dollar spent at a Starwood property gets you two points.
As an added bonus, you'll get up to 25,000 SPG points when you sign up here.. that's up to 8 free hotel stays!