Ebook: The Little Schemer - 4th Edition

If you're an intelligent programmer who wants to know what all the fuss is about with regards to Lisp/Scheme, pick up this book. In a cute question and answer format, you'll jump from finding out if two sets intersect to dealing with the Y combinator rather quickly. If you "get" recursion already, there are still some things to learn here.

Side note: the books recommended in the "Intermission" section are all very good. (-: