On Windows 7 I very quickly got used to use the window snap feature.
You can hold the windows-key and then use the direction keys to snap the window to the side of the screen, and it takes up half of your screen real-estate. I am often comparing window content so I find being easily able to quickly have each window take up half the screen to be very useful.
Back on my XP machine I missed this a lot, until
I found out about Winsplit Revolution [ http://www.winsplit-revolution.com ].
This little app offers a lot more options for snapping your windows not just to a side of the screen taking up 1/2 of it each, but also to the corners (1/4 screen use) and even into two rows of three small windows. This all in seconds, with a nice use of the numpad/arrows to easily and quickly select where in the screen you want the window to go (7 for top left, 3 for bottom right, etc).
It starts automatically on boot, and sits nice and quietly in the system tray, out of the way.
It really is the little things that make the big differences, and once you start using this app you’ll wonder how you ever lived without it.
Check out their demo video at http://www.winsplit-revolution.com/screenshots/videos-demos