The new release by MoFi on their 'One Step' process from Muddy Water, 'Folk Singer' is probably the best sounding blues album I have heard. If you can source one, it is a great listen, not just for SQ, but for music as well.
I would add to the CD list above, which are all excellent, the following:
Little Hatch, 'Rock with me baby'. This one is extraordinary.