I lived in Nashville for two years, and LOVED it. You can easily spend a long weekend just around the area. Go see a Titans game, or watch the Vandy undergrads get loaded and dressed to the 9's (really, they get all dolled up, the guys and the gals) for a Commodores game. Hit the Bluebird Cafe, the best music venue for songwriters, in the history of songwriter/singer cafes. Go dance in some honkeytonk bars in the downtown (Ymo, help me out -- Purple Orchid? Is that the main one?) The downtown area has some fantastic restaurants, and quite a few shi-shi ones that will make you think you're in Manhatten.
Andrew Jackson's "Hermitage" is nearby for some historical/educational purposes, and the Tenn. State museum is pretty interesting -- it has a lot on the civil war battles that were fought just outside of town; there's an observatory in a great park just to the west of the city -- also very good hiking trails in there.
The Mammoth Caves in Kentucky are about an hour away; as are the National Corvette Museum, and the Jack Daniels distillery.
Lest some country-music fan beat me about the head and shoulders for neglecting it, there's also the Grand Old Opry (aka Gaylord Hotels' tourist trap.) I suppose it's worth going to for the music, but I never did. (I prefer the old Ryman Auditorium, where the Opry started.) Near the Opry is a huge mega-outlet mall and a huge hotel with really amazing Christmas decorations, but I wouldn't recommend either unless you're into shopping and schmaltz.