Lisp or Scheme in General
Common Lisp Hyperspec
It's meant to be used with SLIME.
Downloaded from http://www.lispworks.com/documentation/common-lisp.html.
The Scheme Programming Language
Hyperpolyglot: famous Lisp dialects comparisons
This is mostly a syntax level comparison, superficial but very thorough.
One of the definitive sources of Lisp history.