My email inbox is often overflowing. I recently started doing something that has helped a great deal! I receive many advertising emails from companies that I've done business with, or requested information from in the past. Often I am interested in these emails, but I don't want them cluttering up my box for years.
I have always loved the filter and label capabilities of gmail. It's one of the reasons that I primarily use my gmail account these days.
I created a label called simply "ADS." Whenever I receive an email that is advertising, I set up a new filter so that all future emails from that address are labeled ADS. Once a week or so, I simply call up all the ADS and hit delete. If I'm going to act on a specific email (those containing coupon codes, for instance) I usually have done something within a couple days.
This has cut down on the clutter in my inbox significantly!