Personal productivity tip

We all have lots of ways to think about improving our productivity. I like the ideas I read at 43 Folders. I've gotten my first PDA from that site (free, for I had all the pieces lying around the office), and I've discovered do-it-yourself add-ons to make it more useful. From that site, I found a link to off-the-shelf (or -printer) add-ons.

What cool tools do you use to improve your personal productivity?