From everything I understand a credit card is a great way to establish credit which is needed for many situations (buying a house, car, etc). I have had a credit card since I was 16-thanks to my dad who taught be how to use it correctly.
I have a GAP visa card that at the time I got for a discount on a purchase but it was the best thing I ever did. I had a much higher limit available which really helped compared to my other card. I don't shop a lot but this is how I see it..when I have that urge to buy myself a little something-I use the GAP rewards and get myself something on sale..a shirt, underwear..whatever! Plus I know in the future when I have kids I can use it at gap kids/baby too.
If Gap isn't your thing the bank america card with the rewards sounds like a great deal.
Another suggestion-I know some people only use their credit card for a specific thing..like gas (or emergencies when necessary). This might help you stay in check with what your spending. Don't look at the card and think "free money" because it isn't!