keyplyr - 4:22 am on Dec 11, 2012 (gmt 0)
Most of us block unfavorable companies by IP range along with a UA list of tools (downloaders, email address scrapers, etc) that anyone can use.
For a true whilte list, you have a list of allowed browsers and bots (verified IP ranges and/or header info) then block everything else. This takes a higher level of programing skill.
Difficult to post a list since not all are unfavorable to everyone.