(thunder valley mx) in livingston TN, (meadow creek mx) in crossville TN, (800 mx) wich is my favorite, and (TMT-MX park) in moneagle are the one's that i know of. i have phone#s to the tracks or www.hometownmotocross.com
I have been to Exit 143 and right now it is not all the great. The trails are really open and look like they where just run over buy a bulldozer. They have some hills out there to climb but it will be some time before that place gets big at all. There is a MX track in between Ripley and Halls T.N. named Hidden Valley raceway. I just went there last weekend and it was only 10 bucks to ride all day (practice). The track there is 1.2 mile laps. There is also Land Between the Lakes (LBL), it is more near Nashville then Memphis. It is 15 bucks for a 3 day pass and the riding is not all that bad. It is trails but they are the kind of trails where you can ride them in 3rd and 4th gear rollin. The is also a new MX track actually in Memphis on Pleasent view Rd. Behind a car dealership, I have only rode out there to check it out, never ridden on the track. Looks nice and friendly to beginners. And if you really want to go tear your stuff up, you can go to a place called Sugar Creek. It has trails, steep hills, creek bed, and a MX track out there. Nothing out there is really mainted at all but it is some where to ride. It is in Millington I think (10 bucks to ride).
A couple off weekends ago Laretia Lenn's was open to ride at. We went out there and it was fun but there were so many dirtbikes it was not even funny. The only problem I have with riding most of these places is that there are rocks and lots of them.