I can speak for the far western end. In Paducah there is a very active club - Chain Reaction Cycling Club - that has a few organized rides a week. Everything from "No One Left Behind" to some serious speed. For mountain biking we have an intense trail system in nearby Livingston County, and more gravel you can ride in the Land Between The Lakes recreation area, as well as some single track loops in the LBL. Four LBSs, three big dealers with excellent service and one independent shop that works on anything you can bring him.

I hope that helps, and if you need more info PM me and I will find the answer for you.