Google Mail - Send & Archive
Because of these facts, one of the Google Mail features I don't think I could survive without is the Send & Archive. The ability to - with ONE click - reply to an email and archive it saves me about 3 seconds per email...which adds up quickly!
Look under the General tab, about half way down to find the option to turn on this feature -
Once enabled, you will have an additional send button that is blue - this one will send your reply and archive the email out of your mailbox -