US Airways is offering 10 Dividend Miles per dollar spent with Enterprise Car Rental when you rent between now and December 15th and pay with your US Airways Mastercard. You must register here. Pretty solid, especially for Enterprise.
That said, it’s not the best car rental deal out there for US Airways: Rent with Avis for 3 days or more between now and February 28, 2013, and you’ll get 3,000 bonus Dividend Miles. Details here.
You don’t have a US Airways credit card? That’s a big miss. 40,000 miles after first purchase and annual fee waived the first year. Why wouldn’t you get that? Details here.