I find 'Blues' is one of the musical areas that no matter who you listen to and who you think is briliant, someone else will always introduce you to an artist that you've never heard of who will blow you away.
I guess my blues knowledge would be concidered mainstream, but for what its worth my favorites would be
Gary Moore, Jeff Healey, Kenny Wayne Sheppard, Johnny Lang. Some rather more unknowns, Bernie Marsden, Snowey White, Mickey Moody.
Someone i came across in BB Kings Blues Club in Memphis a few years ago. Chris Cain, absolutely brilliant. I have since brought or borrowed/copied everything i could find on this guy. Here is his web page
http://www.chriscain.cc/index.htmlSome other good web poges with mp3 downloads
http://www.berniemarsden.co.uk/home.htmhttp://www.jeffhealey.com/home.htm
