I lost / forgot my Microsoft Office Product Key / Serial Numbere. How can i find it on my computer?

I friend called me today. He wanted to re-install his Computer, but was able to find his Office 2010 product key any more.

How-I-fixed-it:

Using the Freeware Tool ProduKey by NirSoft you can read out the Product Keys or Serials of many Microsoft products installed on your Computer.
http://www.nirsoft.net/utils/product_cd_key_viewer.html

Here's a list of supported programs:

Microsoft Windows 98/ME

Microsoft Windows 2000

Microsoft Windows NT

Microsoft Windows XP

Microsoft Windows Vista

Microsoft Windows Server 2003

Microsoft Windows 7 (Doesn't work with Microsoft Volume Licensing)

Microsoft Windows 8 (Doesn't work with Microsoft Volume Licensing)

Microsoft Office 2000 (Only ProductID is displayed)

Microsoft Office 2003

Microsoft Office 2007

Microsoft Office 2010

Microsoft SQL Server 2000

Microsoft SQL Server 2005

Microsoft Exchange Server 2000

Microsoft Exchange Server 2003

Visual Studio