Frequent Flyer Programs

I'm a little embarrassed to say that for the 6 years I've been living in the UK and the 15 or so trips I've made to the US (not including little excursions around Europe), I have benefitted from these travels only through my experiences, and my bank account has only suffered.

I'm currently looking at another trip around Easter and would like to capitalise on my travel. I mainly fly to Central New York state and to Minneapolis, which is a Delta hub.  I've been eyeing the Delta program, which looks like you can only earn miles by flying and staying at select hotels.  Can anybody recommend a frequent flyer program that lets you earn miles by making purchases?

I'm confused as to what you are looking for. Do you want a credit card that credits you with miles as you use it?

I think most airlines have credit cards linked to their miles programs. Im in British Airways' program and I think they have a credit card, though I couldn't say for sure.  I can tell you that with British airways, one round trip long haul flight generally earns you a free round trip short haul. Not sure how that compares to other airlines though.

What about just getting a credit card with a good rewards structure so you can use it on whatever you like? I have a capital one venture card (one with an annual fee) that earns 2% on everything. I can redeem my points through account credit or by "erasing" purchases on my statement.