G'day folks. I'm trying to introduce Ruby at work, and a few people are interested. However, I've been asked to present the benefits of Ruby over Python and PHP.
I've broken this down into 2 parts:
1) show Python and Ruby's advantages over PHP;
2) show Ruby's advantages over Python.
The first is easy. I'll explain things like:

Everything's an object.
Python and Ruby are easier to read and write.

For the second, I'm thinking of:

Ruby has many conveniences, which makes it easier to read and write. Eg: Optional brackets, and being able to open built-ins, allows for things like 2.days.from_now
RSpec is miles ahead of Python's TDD and BDD frameworks.
GitHub and RubyForge are fantastic resources for finding, releasing, and collaborating on software.

Do you have any suggestions? I'm all ears!
If you really want to show Ruby is better (assuming it is for your application!), why not try writing a small app from scratch in front of them? It doesn't have to be big, but something relavent to what you'll eventually be using it for is a good idea.
Write the app in all three languages including any configuration for the server (I'm assuming you're writing a web app here using DJango / Rails / PHP right?) and show how much faster you are, how much cleaner the code is etc. ...assuming it is ;-)
You can finish up by asking them what they'd like to add to it and then try adding that feature if it's a small change. Nothing like a bit of audience participation - people like applauding themselves. If you get them involved they're more likely to accept the winner.
For the record, I've tried all three and would agree that both Ruby and Python seem to result in cleaner code. I'd go for Python over Ruby though - there was something clunky about the syntax of Ruby when I tried it that I just didn't experience with Python.
Convincing others of Ruby over Python and PHP