Blues "must have, top 100" list?

Many fine suggestions above. At your news stand at this moment is the most recent Mojo "Classic Blues Heroes" issue (volume 1, issue 3) with Eric Clapton on the cover. Inside you'll see aricles on many of those mentioned above and more. Mojo is a British music mag that is well researched and written. Just in time for your post!
I'm a Lightnin Hopkins fan all the way. Did anyone mention Elizabeth Cotten?
Happy hunting!

I agree with just about every selection recommended so far (especially Muddy Waters Folksinger), and would add the beautifully mastered and packaged set on John Fahey's Revenant label: "Screamin' and Hollerin' The Blues--The Worlds of Charley Patton." Not only is Patton represented in this 7-CD set, but so are such Delta greats as Son House, Bukka White, Willie Brown and Tommy Johnson. Essential listening.

I will be much poorer after working through all the suggestions.

Thanks to all for the great posts.

I also like the Bluenose's recommendation of Philadelphia Jerry Ricks "Empty Bottle Blues": nice album.

Ivyinvestor, here's a link to the Willie Dixon: The Blues Every Which Way LP:
http://store.acousticsounds.com/browse_detail.cfm?Title_ID=13302
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Ooop's. Forgot Freddie King. I'm goin' down!!