Structure and Interpretation of Computer Programs
Somebody at MIT was nice enough to make available the videos for lectures on Structure and Interpretation of Computer Programs, by Abelson and Sussman.
It's a refresher in just how powerful Lisp is. For a language approaching 50 years old, it's pretty amazing.
I always crack up a little when I think about the reasons Lisp and Smalltalk couldn't go "mainstream" - why, they use too many resources! (My web browser looks like it's running in 41 meg so I can type into a non-styled text box. I doubt Lisp or Smalltalk would do worse than that:)
Anyway, if you've never studied Lisp, these lectuers are a good excuse for trying it out.