Ground Transportation: There are 3 transportation options other than renting a car. I wouldn't rent a car due to the time and extra frustration that goes with it, as well as learning your way around downtown and the valet parking charges at the hotel.

Metro Transit Authority Express bus service to downtown Nashville: The Nashville Metropolitan Transit Authority (MTA) has a bus route that serves the airport. Route 18 - Elm Hill Pike/Airport has service to downtown Nashville and departs nine times each weekday and four times daily on Saturday and Sunday. The price for a one-way fare is $1.25, and the schedule for this route is available at the Welcome Center, located on the baggage claim level. 615-862-5950 or www.nashvillemta.org
Cabs are $22 each way to/from the downtown hotels. http://www.flynashville.com/ground_trans/taxi.cfm
Gray Line Airport Express ($18 round trip) runs very 15-20 minutes from the airport to 8 of the downtown hotels. Reservations are not required for the service from the Airport, but you should make a reservation for the return trip. http://www.graylinenashville.com/page.cfm?ID=1337