Server side Scripting = Python/Ruby are both sensible choices. I prefer Ruby as a language but Python is a safer choice given the library support and performance. The exception is server/cloud management for which Ruby still has an edge (debatable, I know).
GUI/Desktop Clients, Python + QT. Great combination. Its possible to use QT with Ruby, it just doesnt feel right though.
OSX/IoS/Android - Ruby/Rubymotion. Really, really nice if you're developing for the Apple side. Android support is early days.
BTW I said I'm a Ruby guy but I've 10 years of Python experience. If the project is suitable though I'm more productive with Ruby (with 18 months experience) but it really is a case of the right tool for the right job.