Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
PodKoi - Find podcasts to be interviewed on & guests to interview.
Facebook Local - Discover places to go and events happening near you
PodBooker - The easiest way to get booked on podcasts
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Speaker Directory by HeySummit - Guests for your next event or podcast (or submit yourself!)