I think a lot depends on what areas of computer science you're interested in. If you want to expand more into lower level stuff, operating systems, command line programs, server internals, etc. then Id say go right to c and skip over c++. But if you want to learn more about gaming or desktop apps then c++ or java is probably a good choice. If you want to stay in the networking/web stack but expand your horizons as far as programming theory and development workflows I'd say give either Ruby or Golang a try both have their own unique approaches to problems and IMHO very innovative ways of solving a lot of programming problems.

Best of luck!