Unlocker

Sometimes you are stuck by not able to delete the file because some application unknown to you is holding the file lock. This freeware (Unlocker) helps you in those scenarios. I haven’t tried it yet, use it at your own risk !

What looked impressive for me is the GUI listing of all applications having locks over files in a folder:

6/November/2013 Update: The download link has been changed from ccollomb.free.fr to Emptyloop. You can now go to the Wikipedia page for Unlocker .