Event volunteers registration module
I've used the Webform module for this situation in the past.   Just create a name and email component!


  Webform is the module for making surveys in Drupal. After a submission, users may be sent an e-mail "receipt" as well as sending a notification to administrators. Results can be exported into Excel or other spreadsheet applications. Webform also provides some basic statistical review and has and extensive API for expanding its features.