Hya,
I was on a site that takes security very seriously like we do. Here is a list of Useragents in a txt file:
http://www.0x000000.com/ht.txt
Next is a list of ten of spam bot agents which SHOULD be BLOCKED.
http://johannburkard.de/blog/www/spam/The-top-10-spam-bot-user-agents-you-MUST-block-NOW.html
;D