In my study of the Scala language, I've taken a slight detour to spend some time learning the CLISP implementation of Common Lisp, which I think will help me to better understand Scala itself (as well as fundamental concepts of any Functional Language).
Here are some of the resource links that I've found useful:
A Concise Introduction to LISP, by David L. Matuszek
Common Lisp the Language, 2nd Edition
by Guy L. Steele Jr.
Peter Siebel's, Practical Common Lisp
6 Problems (with solutions in Lisp)
CS107 Handout 53, Autumn 2000 November 30, 2000, Lisp Section Examples
Nick Parlante's http://www-cs-staff.stanford.edu/~nick/compdocs/LISP_Examples.pdf
This is Abhishek Reddy's really well written, concise, summary of the the features in Common Lisp: http://abhishek.geek.nz/docs/features-of-common-lisp
...as well as his: http://abhishek.geek.nz/docs/lisp-answers/
Although not specific to Scala or Lisp, I enjoyed reading this 376 page text...
Programming Languages: Application and Interpretation
By: Shriram Krishnamurthi