Airline Credit Card - 1 mile per dollar spent

This is probably the easiest way to earn mileage in the country, as long as you have credit. Most airlines have partnered with a bank or financial institution to have a mileage earning credit card. There are multiple different view points on how this should be utilized, and some content it is better to get a points credit card that is not associated with one particular airline, to give you more opportunity to earn.

Here is my take:
Determine where you want to go, and how you want to earn that trip. If the answer to your question is, I am willing to go anywhere, then the open option is best. If you have a specific location, look at which airlines serve that place, and build your points based on this desired locale. I choose to remain loyal to the One World Alliance, as I lived in two of its major hubs (Australia with Qantas and Texas with American). You may also make this determination based on which credit card company you already have in your wallet.

Here are a couple offers that are hard to pass up:

40,000 American Airline Miles from Citibank
10,000 American Airline Miles from Citibank Debit
20,000 Alaskan Airline Miles from Bank of America
20,000 Continental OnePass miles from Chase
16 Southwest Rapid Rewards Credits from Chase
17,500 United Miles from Chase

Also, I would highly recommend the Starwood American Express card as well. This will earn you 10,000 Starwood points, which would equate to 3 free nights. So with applying for a credit card from the airline and one from the hotel, you could essentially receive a free weekend vacation.