I wrote a script today that basically goes through and finds all websites on our servers and displays the ones that have Joomla and what version of Joomla it has installed.
Example Output:
Retrieving Site List…
[http://www.breweryarts.org] [Mambo] [4.5.4]
[http://www.artbyblair.com] [Mambo] [4.5.4]
[http://www.budgaugh.com] [Joomla!] [1.0.13]
[http://www.ecomadness.com] [Joomla!] [1.0.15]
[http://www.janusstudio.com] [Joomla!] [1.0.11]
[http://www.sharonchandler.com] [Mambo] [4.5.4]
See code below: