The 3 Programming Languages you need to Know
Hey you kids, get off my lawn!  1960s:  
  Happiness Language:    Lisp
  Hack-it-out Language:  Assembly
  Bread and Butter:      COBOL
  
  1970s:
  Happiness Language:    Lisp
  Hack-it-out Language:  FORTRAN
  Bread and Butter:      BASIC

  1980s:  
  Happiness Language:    Lisp
  Hack-it-out Language:  C
  Bread and Butter:      QBasic

  1990s:
  Happiness Language:    Lisp
  Hack-it-out Language:  C++
  Bread and Butter:      Visual Basic
  
  2000s:
  Happiness Language:    Lisp
  Hack-it-out Language:  C#
  Bread and Butter:      PHP

  2010s:
  Happiness Language:    Lisp
  Hack-it-out Language:  Python
  Bread and Butter:      Ruby

[EDIT: Added "s" to change significance from year to decade.]