C# and Ruby. Demand is running way ahead of supply for Ruby on Rails developers currently.
1) Java
2) More Java
I’ll second C# and Ruby as well as a firm grounding in C and C++.
C# when used with ASP.Net is also leaps and bounds above any web app done in Java.
C# has also developed delegates to replace method/object pointers and dynamic typing that makes possible dynamic type arrays which breaks arrays away from single typing.
C# has also revived pointers which provides the flexibility and more efficient processing that used to be available only in C/C++.
C++ is still the most versatile with capability to customize down to bit level manipulation.
I would recommend C++ for the simple reason that it is one of the more difficult to learn. However, it is not impossible, there is LOTS of support on Youtube and the Internet. Enough so that if all you had was an Internet connection and a PC, it is possible to learn it by your own research.
Also, once you master the concepts of C++, the rest of the languages will be easier. If you live / work in a Unix world, PERL would be a good supporting language.
Just my .02