If you're like me, and you use your email in-box as your to-do list, you need Boomerang, by Baydin. This product literally changed my work life. It's an add-in to Outlook (available for 2003, 2007 and 2010) which lets you move items out of your in-box for a time period you specify - one hour, two hours, etc. - and sends them back to you when the time is up. After a few days of using the trial version, I couldn't imagine life without it.
My use case is this: when I receive a message that's not urgent, but which is something I do want to give attention to (such as a link to an article I'd like to read but can't read right at the moment), I right-click and boomerang it out, and then go on handling the more pressing messages. The email reappears in an unread state at a time when I'm more likely to be able to focus on it. As simple as that.
It costs $14.95, and if you download the free trial first, you may have an option to purchase at a reduced price. (That's how it worked when I tried it.) I got great follow-up and support on the product after my trial, as well.
Baydin is a company to watch. Their Unsearch product, also for the email in-box, recently won the Launchpad competition at the Enterprise 2.0 conference. I signed up to test the beta, and if it's as effective as Boomerang, I'm going to start campaigning for a shorter work day.