I have been using a browser extension for GMail called ActiveInbox. I love it. It’s based on David Allen’s Getting Things Done. It works great in Chrome (you are using Chrome, aren’t you?). Assign an email to a project with one click, or find all emails associated with that project. It’s free, so if you are having trouble managing your mail, give it a try–http://www.activeinboxhq.com/

“Clean out your inbox, transform emails into trackable actions, group them into manageable projects and guarantee every important email gets done.”