The people who run
http://www.alsscan.com (good site) run a password protection script for webmasters at
http://www.realtimepms.com/features.html
It costs $5000. Is it me or is this a bit much? You can get a quality protection system for under $100.
I will say this though - on the list of compromised passwords somebody posted earlier there was only one for alsscan.com and it didn't work for me so maybe it really is good?