One of the most common requests I get when creating a client's blog is an event calendar. If you are speaking or appearing at events a calendar is a great way to keep your audience up to date. A calendar full of events sends the message that you are active and actually doing things.
We've tested and used a lot of calendar plugins for WordPress and in my opinion this one is the best:
It utilizes custom post types for events, which is (in my opinion) the right way to do it. It supports all the event-related fields you commonly could need as well as the ability to display a Google map.