I think this difficulty to make a strong point towards a single other language is that the area where languages excel are usually populated by multiple languages.
Do you want to look at a good object oriented language? Take a look at one of Python, Java, C#, Ruby and probably Perl with the right modules.
Do you want to take a good look at functional programming? Look at one of Haskell, OCaml, SML or something along these line.
Do you want something to prototype rapidly? Python, Ruby, probably Scala.
Do you want web programming? Ruby on Rails, Django, PHP, one of those.
Do you want embedded programming? Well.. look at C. Or C++ with C embedded, as some maniacs use it.
Do you want to look at a good object oriented language? Take a look at one of Python, Java, C#, Ruby and probably Perl with the right modules.
Do you want to take a good look at functional programming? Look at one of Haskell, OCaml, SML or something along these line.
Do you want something to prototype rapidly? Python, Ruby, probably Scala.
Do you want web programming? Ruby on Rails, Django, PHP, one of those.
Do you want embedded programming? Well.. look at C. Or C++ with C embedded, as some maniacs use it.