Do find yourself typing the same message over and over, perhaps a weekly reminder for for homework, projects, progress reports, or office hours; a form letter to parents; FAQ; or a standard meeting agenda? Google Mail has the answer. Canned Responses is a Lab that allows you to insert pre-formatted content you create into your messages.
To enable Canned Responses, click on the gear in the upper right of the Google Mail window, select Mail Settings, and click on the Labs link. Scroll down through the Labs (alpha order) to locate Canned Responses. You can also enter "canned" in the Labs search field to show the Canned Responses Lab. Click the Enable radio button. Finally, at the top or bottom of the window, click the Save Changes button. Canned Responses will be enabled and you'll be returned to Google Mail.
After enabling Canned Responses, watch how to create a "New Canned Response" and "Inserting a Canned Response."
After enabling, to create a Canned Response, click on the Compose mail button. Enter a subject in the Subject field and what you want to say in the message body. Next, click on the Canned responses link below the subject and choose Save > New canned response. Since this is your first Canned Response, it's the only choice you have. The Canned Response title will be the subject you entered (although you can edit this). Click the OK button.
To use a Canned Response, click the Compose mail button. In the message window, click the Canned responses link and choose Insert > [canned response title]. Once inserted, you can edit (as needed). You can also insert Canned Responses when replying or forwarding messages.
Notes: You could create custom signatures as Canned Responses. If you like to send messages in a particular color/front/size, you could create a Canned Response with one start-up word formatted the way you want. Then, when you compose mail, choose that Canned Response, double-click on the start-up word, and start typing.