Insert a calendar invitation
Since my friends share their schedules with me in Google Calendar, when I want to see a movie with them, I can check to see which nights they're free before sending out an email about it. However, I need to switch between Gmail and Calendar in order to check their availability and send an email invitation.
Today, we're launching a new feature that brings tighter integration between Gmail and Calendar, making it easier to create Calendar events from within Gmail. When you compose an email message, there's now an "Insert: Invitation" link right under the subject line.
You can check your friends' availability and choose an appropriate time for the event you're setting up right from there. When you've settled on the details of the event, click the "Insert Invitation" button and a preview of the invitation will appear in your email message: