Convincing others of Ruby over Python and PHP
Devil's advocate maybe...


Everything's an object.


This is a feature of Ruby, but it is not self-explanatory as to why this is a benefit.  You would need to pre-prepare an argument for why that is a benefit.  When convincing somebody of something's superiority, always think in terms of showing the benefits, not the features.


Python and Ruby are easier to read and write.


This is a very big claim to make, and I would not be comfortable making such a claim without a substantial amount of credible objective third party evidence supporting this.  If not, and I suspect such a claim really couldn't be backed up, I would play it safe and avoid making such a claim.  Making a claim this substantial, but only backing it up with personal opinion or anecdotal evidence would not be a good idea.


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


Again, you will need to think benefits, not features.  It may be true that it has optional brackets, but you cannot just mention a feature, you have to explain its benefit - why that feature is a better idea than any other approach.  Personally I am not sure that 'optional' syntax is ever a good idea, and would need a fair bit of evidence to convince me that it was.


GitHub and RubyForge are fantastic resources for finding,
  releasing, and collaborating on
  software.


That's good.  There are also similar resources for languages other than Ruby - again, you will need to not only mention the existence of these but explain how they are better than the alternatives.
Good luck.
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!