Perl (scripting, CGI)
C# (Microsoft, Java like)
C++ (Visual Studio)
Ruby (Scripting, CGI)
Snobol (string manipulator)
Cobol (historical)
Fortran (historical)
Visual Basic (GUI's)
Basic (historic)
Ada
Lisp (parentheses, parentheses, parentheses)
Smalltalk (pure OO)
APL (matrix/vector manipulator)
Oberon (create types)
ML
Turing (theory)
VRML (3D scripting)
Scheme (lisp like)
Pascal
Modula-2 - (Pascal like)
Logo (turn your turtle)
XML (markup)
UML (modeling)
Lagoona (OO)
Algol (structured language)
Forth (stack oriented)
Prolog
BF - In case you've never come across BF, it is a very simple but Turing-complete language that will quite likely hurt your brain if you try to write non-trivial programs with it. More information is available at http://www.catseye.mb.ca/esoteric/bf/ The B stands for Brain, the F stands for something else. Some people have too much time on their hands.

I would like to do some programs for some old Commodore 64's, or Atari systems, but I don't think I can find an emulator.