Call for geek help: scripting languages

I'm teaching a Survey of Programming Languages course in the fall. The goals of the course are to teach students how to learn a language, and to introduce students to ideas and techniques they didn't see in their first-year Java courses; if they happen to learn a language that gets them a job, that's a bonus. They're familiar with (if not necessarily good at) class-based OOP and imperative programming; they haven't seen higher-order functions, closures, continuations, comprehensions, macros, or declarative programming in general. Most of them haven't seen any kind of parallel or multithreaded programming, nor network programming.

Traditionally, this course has been about 50% C++, 25% Scheme, and 25% Prolog, but the C++ content has been moved to another course. After polling the preregistered students by e-mail, I've decided to fill the gap with some reasonably-modern scripting language. Leading candidates so far are PHP, Python, Ruby, Lua, Erlang, and Scala.

I can make an unbiased choice among these because I don't really know any of them (although I've written some PHP-based server-side web scripts). So I'll be learning them just ahead of the students :-)

Any advice?

Par-Tay!

In today's mail, a letter from the State of New York saying I miscomputed our income tax and we get an unexpected refund.

Two dollars and sixty six cents.

Vegas, here we come!