One often overlooked aspect of using your computer productively is the desktop. Instead of having a pretty picture of the beach, try using one of these wallpapers.
EZ Access Desktops
If you’re a fan of the GTD (Getting Things Done) methodology, this is the wallpaper for you. Grab it (or one of the others) from here.
Available in both light and dark, the Layered Desktop wallpapers allow you to group your icons by categories.
Similar to the EZ Access Desktops, the panel method outlined here allows you to group icons according to category.
Lifehacker explains how to use Google Calendar as your Desktop Wallpaper in Windows.