RSVPmaker is an event scheduling and RSVP tracking plugin for WordPress, using the custom post types feature introduced in WP3.0 to track events as an alternate post type with associated dates.
Site editors and administrators have the option to request RSVPs for any given event and specify an email address for notifications when someone responds. RSVP Reports can also be run from the administrator’s dashboard.
If a fee is to be charged for the event, RSVPMaker can collect payments online using PayPal (requires manual setup of a PayPal account and creation of a configuration file with API credentials).
Home Page: RSVPmaker.com
WordPress Repository: http://wordpress.org/extend/plugins/rsvpmaker/