The following are links to the various clubs that sanction/license agility trials in the US. These links should take you to the event listing page for the organization. Note, if a link breaks, use the "Info Request" to send a message to the webmaster so we can fix the link.
Note, if you register (free) with the AKC site, you can save searches (the "manage searches" tab) to expedite frequent searches. For example, you can set up a search that will list all future trials for MD, DE, VA, PA, depending on how far you are willing to travel.