It takes a little bit of work and you have to plan ahead, but I buy AA gift cards and get 4 miles per dollar spent. Use the Aadvantage eshopping portal to buy the cards from giftcertificates.com and get 3 miles per dollar spent plus the 1 mile from CitiAA (they don't take Amex). The cards come in denominations up to $250 and there is a small fee for shipping so the best way to do it is to buy one of their super certificates for as much as you can (i do $2,000 to $4,000 at a time to pay for work trips) and then have them ship me everything in $250 cards. You can then enter the gift cards at purchase on AA.com

Like I said, it takes a bit of work and lead time, but until CitiAA starts paying more miles for AA purchases like UA does, it's the best way I've found to maximize miles.