The Github repository crawler-user-agents contains a list of of HTTP user-agents used by robots/crawlers/spiders. I regularly maintain this list based on my own logs. I do welcome additions contributed as pull requests.

The pull requests should:

• contain few additions (say less than 5)
• specify a discriminant relevant syntactic fragment (for example "totobot" and not "Mozilla/5 totobot v20131212.alpha1")
• contain the pattern (generic regular expression), the discovery date (year/month/day) and the official url of the robot
• result in a valid JSON file (don't forget the comma between items)

Example:

{
  "pattern": "rogerbot", 
  "addition_date": "2014/02/28", 
  "url": "http://moz.com/help/pro/what-is-rogerbot-"
}

The list is under a CC-SA license.

--Martin