SpeedPagan: not sure where you live, but i'll second the mention of USMTS for a touring series here in the Midwest.
check out youtube for a TV series from a couple of seasons ago called "Dirt Knights".
also as mentioned, most of the local dirt tracks have modifieds sanctioned by imca, ump, usra, etc.. with rules close enough among them that there is a lot of crossover.
usually great racing with very talented drivers at the top.