I need a list of companies who are putting on business events (e.g. a
webinar or a user conference or a live seminar).  Any suggestions?

Hi! Thanks for the question.

The following links provides list of companies that put up business events.

Yahoo Directory
http://dir.yahoo.com/Business_and_Economy/Business_to_Business/Event_Planning_and_Production/Corporate_Events/

DMOZ Directory
http://dmoz.org/Business/Business_Services/Event_Planning_and_Production/Planning_and_Management/

Corporate Event Channel
http://www.corporateeventchannel.com/event-planners.htm

PR.com
http://www.pr.com/business-directory/194


Search terms used:  
"corporate event" planners directory

I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
                                                          
                              
Regards,                              
Easterangel-ga                              
Google Answers Researcher