Because I found it extremely difficult to locate the user agent / bot names of the various big search engines, I’ve decided to list them here:

Google User Agents:

• Googlebot: crawl pages from our web index and our news index
• Googlebot-Mobile: crawls pages for our mobile index
• Googlebot-Image: crawls pages for our image index
• Mediapartners-Google: crawls pages to determine AdSense content. We only use this bot to crawl your site if AdSense ads are displayed on your site.
• Adsbot-Google: crawls pages to measure AdWords landing page quality. We only use this bot if you use Google AdWords to advertise your site.

Yahoo User Agent:

• Slurp

MSN / Bing User Agents:

• MSNBot Main web crawler (www.live.com)
• MSNBot-Media Images & all other media (images.live.com)
• MSNBot-NewsBlogs News and blogs (search.live.com/news)
• MSNBot-Products Products & shopping (products.live.com)
• MSNBot-Academic Academic search (academic.live.com)

ASK / Teoma:

• Mozilla/2.0

Alexa / The Internet Archive:

• ia_archiver
• ia_archiver-web.archive.org
• ia_archiver/1.6