As far as I know, every major airline has a free card that gives 1/$2. If you already have American miles, probably best to build on them instead of starting another airline, provided American is easily accessible to you at your airport.

Personally I prefer the Starwood AMEX, which can transfer its points to almost all of the airlines 1-1 and is free 1 year then has a fee, but if you are in college and do not charge that much per month, the fee may not be worth it for you.

Even if you do not see a free card advertised, I think that they all have them, just call the same number as for the regular card and ask about a no fee card that gives 1 mile per $2. Make sure that you get a bonus for signing up, I think it is usually like 2500 or 3000 miles.