Top of my list would include: Merle Haggard, Waylon Jennings, Willie Nelson, Johnny Cash, Kris Kristofferson, and lots more I can't think of right now.

I like some of the newer stuff (Kenny Chesney, Toby Keith, etc.), and but I think a lot of what gets played on the radio now is just pop crap. (I've also noticed that when I've been in other parts of the US, country radio seems better than it does in the northeast, especially Boston.)