Depending on your spending habits a mix of the following is recommended:

The Starwood American Express Card (20,000 points = 25,000 AA miles (5,000 miles bonus when you transfer 20,000 points at a time)
The Citibank AAdvantage line of cards (1 point = 1 mile) Platinum doesn't really give you that much increase in benefit over gold, read the details to see if you need it.
I personally really like the Citi AAdvantage Business Card because it gives me two miles for every dollar purchased on american airlines as well as an admiral's club discount. Both of which are very useful to me.

They all have annual fees.