<p>(Mathson here)
Java and Python are good general purpose languages. Java is one of the most common languages for servers in particular. Python is generally thought of as slightly more of a scripting language than Java or C++. If he likes Python he may also want to take a look at Ruby, as they are often used for similar tasks. In either case the syntax is quite similar to C++'s so it should be easier to learn than something like Lisp.</p>
<p>Java and Python both have plenty of books to teach the language. I know that Thinking in Java is pretty good, and it is available online. I learned python by looking through the documentation and reading a few online tutorials, so I don't know of any books in particular.</p>
<p>A word of warning about the computer club. Trying to teach even 5th graders how to program may be very frustrating (it was for me). It might be better to start with one of the programming languages targeted more at kids. For this he could try a version of Logo, the smalltalk-based Squeak or MIT's new one named [url=<a href="http://scratch.mit.edu/pages/download%5DScratch%5B/url">http://scratch.mit.edu/pages/download]Scratch[/url</a>].</p>
<p>Scratch seems very similar to Logo + various turtle languages, but using drag-drop visual components instead of text. Squeak is a complete programming language that isn't entirely targeted at kids, so it might be a bit more difficult.</p>