It depends where you come from.
If you are from the Czech Republic, Estonia, Latvia, Lithuania, Hungary, Poland, Slovenia or Slovakia, you can now work without a work permit anywhere in the EU.
If you are from Romania or Bulgaria, you can work without specific formalities in Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, Greece, Hungary, Italy, Latvia, Lithuania, Poland, Portugal, Romania, Slovakia, Slovenia and Sweden.
Restrictions are still imposed by Austria, Belgium, France, Germany, Iceland, Ireland, Liechtenstein, Luxembourg, Malta, Netherlands, Norway, Switzerland, Spain (only for Romanians) and the United Kingdom. These restrictions concern employed work only – and can only apply until 31 December 2013. No restrictions apply if you are self-employed.