I have recently become interested in - nay, obsessed with - tracking down the most effective way(s) to manage my email inbox, and I wanted to share a couple things that really work for me.

Inbox Zero. Instead of letting my inbox fill up, I process everything at self-established intervals using Merlin Mann's Inbox Zero steps: Delete, Delegate, Respond, Defer and Do. Following these five rules at a regularly scheduled time will ensure a clean inbox. Keep in mind, though... When you choose to defer, you must move that email out of the inbox and create a task for yourself.
Three Folders. I have set up three main email folders: Follow Up, Hold and Archive. When I choose to defer (see above), I simply place the email in the Follow Up folder and create a new task list entry. If I'm waiting on a response before I can complete an item, I place it in the Hold folder. And if I simply need to save the email for future reference, it goes in the Archive folder.
Five Sentences. I try my best to keep email responses to five sentences or less, based on a Web site I discovered a few months ago. Thought I might occasionally run longer, this concept has helped me focus on the structure and purpose of my message: Who am I? What do I want? Why should I get it? When do I want it? I even put a little message about the five sentence philosophy into my email signature so people know I'm being efficient and not rude.

I also noticed recently that Getting Things Done guru David Allen offers a free document, Getting Email Under Control, on his Web site. It isn't groundbreaking, but there are several good ideas and reminders.

How do you keep your email under control?