There is most definitely some good music out there that doesn't get mainstream exposure. Radio is too highly formatted for some music to get a chance because it doesn't fit with in narrowly defined groups, and MTV rarely shows videos anymore and when it does it's even harder to find a rock band. The Drive By Truckers are a prime example of not fitting into a format, but being deserving of wide exposure and not getting it.
For those who want to hear what Little Steven's show is all about (schedule/stations list as well as archives)
http://www.littlestevensundergroundgarage.com/
You are as likely to hear the High Dials, Sugar Shack, Detroit Cobras, or Dirtbombs as you are to hear "classic rock" on this show though (and his 60s playlist includes the Creation and the Pretty Things, unlike traditional "Classic Rock"). Actually I find that to be a good thing.