I found this script on my travels - CrawlTrack. I'm not connected to this script / site in any way but I've been using the script for a week now and thought it was worth a mention.
It tracks and logs bots, crawlers, spiders that visit your site. It is PHP / MySQL based and is absolutely FREE.
Demo:
http://www.crawltrack.fr/crawler/Home:
http://www.crawltrack.fr/
