Gmail Beta now gets auto-reply feature, its called ‘canned response’ in Gmail. Nice catchy name. This feature has been there in Windows Live Hotmail, now this useful feature is also put into Gmail beta.
First enable the feature from settings > labs
Now you can compose your reply once and save the message text with the ‘Canned responses’ button. Later, you can open that same message and send it again and again.
Once you have created some ‘Canned Response’, you can set up filters to send it automatically.