If you have not notice, Google Calendar now has a new feature that will allow you to email guests any event created in your Google calendar. Along with emailing events, you can also add a message before sending.
To email an event, access you Google Calendar and either create an event (if you do not have one you want to email) or click on an event, and then click the edit event details link.
Next, in the Guest section look for the Email guests link in the upper right corner next to the email icon.
The Send an Email Guests window will be displayed, allowing you add a message text or modify the To: list before sending the event. You can also choose to send the event to yourself.
When finished, click Send to send the event. Pretty cool. Thanks Google!