C# is growing. In my opinion, anyone developing windows software should be using it instead of C++ because it avoids many common causes of bugs and security holes. That said, a lot of companies are stuck using C++ because they have an existing code base. C++ was the reigning king for so long that it will take a very long time for it to go away. You shouldn't worry about the market for it going away. And like emboss said, having C++ on your resume means that you actually have some sense how things like resource management and type safty works.
I think the question should come down to domain. Each language has strength in different domains. This is partially because the tools are set up that way. You can get perl working on a web page a lot easier than C++, but its a lot harder to develop a desktop application in perl. This is also a cultural thing. So, think about what you want to do and then look into the languages people are using to do it.
Web on unix/linux systems: Perl, Python, Ruby
Web on windows systems: ASP, vbScript, JavaScript
Cross platform Web Apps: Java
Hardware interface: Assembly, C, C++
Desktop apps on unix/linux: C, C++, Java
Desktop apps on windows: C++, C#, VB
New companies that don't have to worry about an existing code base will tend to use the newer langauges, while older companies will be stuck with the older languages. If you target Ruby or C# you will likely work on new projects, but if you target Perl or C you may end up working on a long established project.
And you really need to learn multiple languages in your career, or you will suffer from
the blub paradox.