This new version of Mailtags is so cool. Most of my work comes into my email box. Finally, I can make these work emails into to do list items quickly, easily and with keywords even. With one click I can see it in my iCal to do list. You can set the priority on the to do. You can assign it to a particular calendar - all in a little pop-out side panel that doesn't get in your way.
You get this fantastic two-way link. When you are in iCal looking at your to do list, you have a URL in the standard pop-out info panel that takes you to the email. Slick! Mailtags is donationware.