a) if you know someone who is a developer, ask them to add your devices UDID to their developer account
b) pay someone online to do this for you, wouldn't trust my UDID with someone I don't know, though
c) pay Apple a fee ($99/year I believe) for a developer account
You should have made sure you had your ducks in a row before installing iOS 5 beta. Had you taken the time to read up on it, you would have realized that you need your UDID registered for your phone to work with the beta software.