I have an idea for Gmail that I'd like to see implemented.

Tags.

Yes, those simple things that have become so popular. I'd like a text field under the message body text box where I can enter tags (words, phrases, links to other emails and sites, etc.) associated with that particular email.

I'd like this to be a separate text field outside of the main message body because sometimes I'd like to add tags that include words not include in my email; plus it's an easy and organized way to keep track of the data in my Gmail account. A tags feature also works well with Gmail's use of a searcheable archive.

You could access this text field by using a link-button similar to the new "Reply on top" link-button available for written messages.