I have to agree with everything said so far. We are truely lucky that so much music has been recorded and so much has been lovingly compiled by people like Yazoo.

It must look like a vast ocean though, to someone who is just starting out. In terms of must-haves I think the distinction between must-have for reference and must-have for listening is good. I suggested Robert Johnson and Muddy Waters because they work for both. Also, their songs have been covered so many times that the music will sound familiar even to someone who is new at the blues.

What has always worked for me is to start with someone I like, find out who influenced them, listend to influences and continue the process. Do this a few times and great patterns begin to emerge.

If you are trying to learn the blues, either country or urban, I would suggest sticking to people who recorded before 1960. Also, (at the risk of setting off the classic debate) avoid white performers like the plague.