Send and Label
Hey, this would be really great and easy to implement:
Just as you can currently "Send and Archive" a message with a single click, you should add the option to "Send and Label as [user selected label] " with a single click.
For example, I currently label the messages that I send and need to follow up with as "Waiting for...". Currently I must send the message, go to the Sent Mail folder and manually label the sent message. With this new feature I could just use the "Send and Label as Waiting For..." and the sent message would get automatically labeled as a message that needs a follow up.