Learning Lisp or Ruby
My favorite technical book of the past year was Practical Common Lisp by Peter Seibel. Believe me, if it could convince me to return to Lisp, it's a well-written book.
However, all the cool kids are learning Ruby. Ruby has some Lisp-like flexibility in comparison to more popular languages like Java and C#, but it doesn't have Lisp's elegance / terseness of syntax. If you want to learn Ruby, the best book is Programming Ruby: The Pragmatic Programmers' Guide, Second Edition.