Nice refresher thread about the types of bots that Google has besides it's regular crawler. I remember when they only had one running around and we watched every time it changed from 2.0 to 2.1 to much fanfare. These days, things are much more complex.
Here is a list of the current Google robots as far as we know:
- MediaBot - used to analyze AdSense pages, user agent "Mediapartners-Google"
- ImageBot - crawling for the Image Search, user agent "GoogleBot-Image"
- AdsBot - checking AdWords landing pages for quality, user agent "AdsBot-Google"
- Generic Mobile Phone (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)
Discuss at WebmasterWorld - Google Bots