Lambda the Ultimate

Of K "fame." His mind is so far out there compared to the way most programmers think and work.

And Chuck Moore (Forth) for similar reasons.

..sounds interesting. I don't usually associate debugging with much beauty.

Unless this is along the lines suggested by Jon Bentley's title: "the most beautiful code I never wrote" -- i.e. its easiest to debug code that doesn't need to exist because you were able to solve a problem in a very simple/elegant way.

[edit: oops, this was supposed be a "comment", not a "reply"]

Go through the ICFP winners, pick one that's particularly nice, and solicit a chapter from one of the authors. (Unfortunately Elliotte Rusty Harold took away most of my proposed chapter title, "Correct, Beautiful, Fast: Pick Three".) I competed in the 2004 contest, and looked at the winning dunkosmiloolump entry afterwards. I thought it was pretty intimidatingly pretty for something banged out by a team under a hard 72 hour deadline. And since the contest has run for many years now, for all I know that is not the most intimidatingly pretty entry.

Also, perhaps it's not code exactly, but how about a chapter on a beautifully simple and powerful algorithmic theme? E.g., skip quadtrees, or Hopcroft partition refinement.

I've found his code remarkably easy to read.

Not all of it is all that easy, but he is a brilliant programmer and his code is highly recommended reading.