Dynamically Assign Member Group on Registration

I believe it would be very useful for have new members assigned a specific member group on registration (not just the default group). - Perhaps based on the registration page URL, or a custom form select. I am developing an event management site and we need to have various different types of participants become members in different groups. Right now it appears that the Super Admin would need to assign each new registrant their group before approving registration. To make things more difficult, New Member Notifications do not include a way to identify which type of new member is registering.