Leadbelly
Howlin' Wolf
BB King
John Lee Hooker
Robert Johnson
T-Bone Walker
There is a little known street performing dude from So Cal named Brother Yusef who is freaking awesome. He has a few albums, I highly recommend them. There is also a Jimi Hendrix blues album that is great. If you just look around at a lot of rock it is full of blues too, especially guys like Led Zeppelin (ie: Can't Quit You Baby), Allman Bros, The White Stripes, and any band Clapton ever had his hand in. Even Muse has a couple of blues tracks.