And of course there is the Windows 7 Aero Snap (Docking) feature! There's a ton of information on Google as to how to do side by side windows, but here's some general directions:
First, be sure your Aero Snap setting is enabled (which is the default), and make sure your windows are not "maximized" to fill the screen. (If a window is maximized, click the "Restore" button near the upper-right corner of the window.)
After that, all you need to do is grab the edges of your windows and resize them, and grab the Title Bar to move them around. You can arrange them any way you like.
If, for example, you'd like to have two application windows tiled on your screen, so each is occupying half the screen, one on the left and one on the right, here's how you can use Aero Snap to get two of them side by side, left and right:
1. Open the first application.
2. Ensure it is not maximized by pressing the "Restore" button (as noted above). It will become smaller and you'll be able to see the Desktop around it.
3. Now move your mouse to the Title Bar at the top of the window, click the mouse and drag that window to the left edge of the screen. Keep dragging until the mouse reaches the edge of the screen and you'll see the outline of the window jump out to the center of the screen. Release the mouse button. The application will now be automatically sized to fill only half the screen.
4. Repeat steps 1 and 2 with the second application.
5. Drag it, as in step 3, but this time to the RIGHT side of the screen.
Voila, two windows tiled side by side on your screen. To return them to their original size and shape, just drag them off the edge again.