Instead of 7 specific languages, I'd give you 7 categories:
A systems language, like C, C++. A managed language, like Java, C#. A weakly typed language, like Python, Lua. A web-server centric language, like PHP, Ruby. An automation language, like Bash, Batch. A functional language, like Erlang, Haskell. A domain-specific language, like SQL, Mathematica.
There is a book called "Seven Languages in Seven Weeks" ...