The following 25 countries are part of the Schengen zone, ie you can travel to all these countries with a Schengen visa:
15 initial Schengen Members (before 2007):
Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain and Sweden
9 countries who joined Schengen in 2007:
Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia
1 country who joined Schengen in 2008:
Switzerland