Python or Ruby for a .NET developer?
What? No mention of IronPython?
IronPython is the flagship language of the DLR. It allows you to use all the familiar .NET libraries, but through Python.
I would definitely try Python and IronPython. You'll learn a lot and might even sneak it into your current projects (you can embed an IronPython engine in a .NET application).
I'm a C# .NET developer and I work on mostly ASP.NET projects.
I want to learn a new programming language,

to improve my programming skills by experiencing a new language, 
to see something different then microsoft environment,
and maybe to think in a different way.

I focus on two languages for my goal. Python and Ruby.

Which one do you offer for me ? 
Pros and cons of them on each other?
Is it worth learning them ?

EDIT : Sorry I editted my post but not inform here, 
Ruby on Rails replaced with Ruby.