This has been discussed on the DansDeals Forums for the past year or so, but it’s good info in case you’re not (yet) a DansDeals Forum user!
Amazon payments lets you send and receive up to $1,000/month per Amazon account without any fees! Send $1,000 to a friend from your credit card and your friend will get $1,000 deposited to their bank account without any fees and you’ll get 1,000 miles or points, and more importantly, be $1,000 closer to that spending threshold you need to meet to get signup bonus miles!
Just be sure to select that the payment is for goods/services and not cash advance when making the payment on Amazon.
This can help you meet thresholds on cards with spend hurdles like the Starwood American Express