Just found a new cool web app fingerprinting tool BlindElephant. It was presented at BlackHat USA 2010.
A really cool tool that computes hashes of files from the target server and compares with the hashes of known versions to identify the webapp version
$./BlindElephant.py http://www.andrewhay.ca/ wordpress
Loaded wordpresswith 159 versions, 599 differentiating paths, and 226 version groups.
Starting BlindElephantfingerprint for version of wordpressat http://www.andrewhay.ca
Fingerprinting resulted in:
Best Guess: 3.0-RC1