[rmckayfleming]

Common Lisp the Language: 2nd Edition by Guy Steele. It's a bit hard to come by as a physical copy (I ordered mine from Abe Books), but it's a fantastic example of technical writing in many facets. I pretty much read it cover to cover (skimming over some of the more reference-y material).

What I found particularly unique about it was the way it highlighted changes made to the language since the first edition. Instead of having a notes section at the back or asides scattered throughout, it's structured like a redlined document (although much easier to read). Paragraphs that are no longer relevant are marked with a dotted vertical line in the margin, while additions are marked with a solid vertical line. Typically you'll see a removed section immediately followed by an addition that'll note something to the effect of "X3J13 voted to remove this from the language in July 1988..." and it'll go on to explain why that happened. Reading about all of the votes really hammered home the fact that Common Lisp was a compromise between many different organizations and dialects. So not only did it help me better understand Common Lisp, it helped me appreciate why Common Lisp is the way it is.