Eli Bendersky's website As I wrote before, one of my purposes for buying a huge 22" wide-screen monitor was to use it as two smaller screens for programming (I like to have at least two editor windows open and visible at the same time).
Windows comes with some basic tiling capabilities. For example, right clicking on the task bar and selecting "Tile Windows Vertically" will tile all currently open (un-minimized) windows side by side. There's a more convenient way I wasn't aware of until lately - you can select multiple windows by holding Ctrl and clicking their task bar rectangles. When you have some windows selected this way (and they will all be colored as "active" on the task bar) right click on one of them and select "Tile Vertically" - it will tile only the selected windows, in the order you've chosen them from left to right.
If you really want powerful tiling capabilities, you'll have to resort to scripting. As I've mentioned once or twice, I'm using Autohotkey windows automation scripts for various tasks. One of the things I like most about Autohotkey is its active and creative user community. If you can think of something that will make you life with Windows easier, just check the forums - someone has probably done it before.
So, it didn't take me long to find WindowPad - a script that provides easy shortcuts for arranging open windows on the screen. Now, having an open window in front of me, all it takes is pressing a Win+Numpad combination (Win is the "Windows" button that is present on most keyboards, somewhere in the area of the left Ctrl and Alt). Win+4 moves the window to the left half of the screen, Win+5 to the right, Win+3 to the right bottom quarter, and so on. Win+5 centers the window with as much width as I've pre-configured, and Win+0 maximizes it. This script is wonderful and is really making my life easier. Now you can arrange the windows on your screen in any way you like, as easily as with a few key presses. And if you have more than one monitor - it supports that too.
