As an Event Marketing professional I highly recommend Event Marketer Magazine, the Event Marketer website (www.eventmarketer.com) and other Red 7 Media publications (i.e. BizBash... a whole NEW world of prospects) to learn more about the heavy-hitters in this field.
For their top 100 Event Marketing Agencies of 2008 visit:
I also recommend checking out those agencies that specialize in branded entertainment and sponsorship activation:
Finally, for a thorough Event Marketing Agency list visit: