Convincing others of Ruby over Python and PHP
Actually no one ever conviced me (at least directly), to use one programming language or another. 
I used to have a certain need for clearness (if you might call it that way) and some other criteria, a language and its ecosystem should meet. And you definitively will end up using some stdlib, and third-party resources, so you might want to look into them as well (and use them as arguments).
I am a fan of both, ruby and python (and these languages conviced me both by their design, their constant progress and their communities). The general notion of a scripting language makes them equally appealing. I found gem to be one of the slowest software I ever used. And personally, I think pythons stdlib is better organized than rubys. But I like Ruby Mixins, they are elegant and safe a lot of time.
In short: You could point your colleagues interest to some current hot spots, where coding is just hard, then show some alternatives in ruby. Rake is a great tool as well, demonstrate it ... Just be rationally passionate about it .. The rest will come ..
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!