Last year I covered a stack of keyboard shortcuts for Windows including some specific to Windows 7. I covered the keyboard shortcuts for snapping windows the the left or right half of the screen 9and hopefully that has come in handy for you). In true form, Microsoft provides another way to do the same thing if you are no good with remembering keyboard shortcuts and prefer using the mouse where possible.
All you need to do is grab the title bar of the desired window and drag it to the left or right side of the screen. You should notice that the outline of the window will expand to fill the corresponding half of the screen at which point you should left go of your left mouse button (or the right button if you use your mouse left-handed). You should find that your window now fill exactly half the screen leaving the other half for more windows or another big window.
I use this personally to have two browser windows side by side on my screen or a document on one side and reference material on the other when I am doing university assignments.