I recently had the opportunity to check out a program online called EventBrite, and man is it awesome!
As long as your event is free, the service is free, but holy smokes you still get all the wonderful functionality: online registration and confirmations, zillions of options when setting up your event, you can schedule emails, your event can be recurring, there are all sorts of nifty reports for after the event, you can print tickets, and on and on and on. Very robust!
If you run events either online or in person and are looking for a program to help you manage your registrations, I would definitely recommend EventBrite.