I wrote an event registration module that integrated with the Geeklog calendar for a client. It allowed the admin to create events that members could register, cancel and view the registration. The admin could easily see who was registered - add/delete from the list. The admin could also send out a group email to all event attendees.
I'm available for contract work and there may be some re-use from the components I have already.
I did a quick mockup of a image to show the screens - have a look
here
Geeklog components by PortalParts -- www.portalparts.com