I created a gmail account just for archive... and I forward a copy of every email to that account (and not delete the original). I then ruthlessly delete almost all email that I receive as soon as I read it. I typically have 2 or 3 emails active in my account at any time. I love having an uncluttered mailbox.
If I later decide I need to see an email that I deleted, I just log into my gmail archive account, and use googles excellent search capability.
/Jim