This week only you can earn 45,000 miles by getting the Gold Delta SkyMiles card from American Express. Normally this card would get you a 25,000 bonus plus 5,000 if you meet a spending minimum. This week they are offering a big bonus that would earn you 45,000 miles. Thats almost enough for 2 domestic flights just for being accepted. However, you must spend $3,000 in the first 3 months so if you have $1,000 in bills a month this is easily doable. Things you are already paying for like groceries, gas, cable, internet, cell phone, and anything else you need to buy. Just use your card and pay off your balance.
There is a $95 annual fee the second year of the card but you can always cancel the card before then. Or just look at it as free checked luggage. If you check luggage a lot and are not a medallion member this fee will pay itself off after just a couple roundtrip flights on Delta since all your bags will check free once you are a cardholder.
Details below from AmEx. Apply here.