One of these days I'm gonna sit down and properly learn Lisp. My career as a programmer is still relatively young ( < 5 years), and learning lisp won't provide any value in my day-to-day work. But understand the concepts and paradigms of Lisp certainly has to have some value.
There's also SICP and Lisp in Small Pieces, maybe also Artificial Intelligence: A Modern Approach, that contain very interesting stuff with Lisp and in general.
Paip is a good and useful one to learn