Be a little careful with the language here.
The MDD is not
a standard. It is a regulation. (Or rather, the transposition of the Directive into Italian law is the regulation).
The MDD (typically) requires that a company implements a quality system. The standard that is accepted as meeting the requirements for that is ISO13485:2003.
But don't buy that. Buy ISO/TR 14969 instead. It is the official guidance for ISO13485, and includes all the standard elements within itself.
GMP simply means "Good Manufacturing Practise". However in some countries, the law requires you to meet that country's interpretation of what it considers GMP to be. In the USA, the law is essentially the QSR/GMP.
Finally, for other standards, you may wish to look at this list
; click the relevant link.