Metropolitan Nashville, Tennessee offers the best and less expensive cab ride to/from Airport, OpryLand, and Downtown - $25.00 for 1 to 6 people. It is way cheaper than shuttles who charge $30+ per person.
Taxi companes and their phone numbers are listed in Yellow page or these are the top rated companies in Nashville, Tennessee.

Sharma Taxi - sharmaTaxi.com (615) 573-2486

Yellow Cab yellowcabnashville.com (615) 256-0101

CheckerCab

Allied Cab -- alliedcab.net