I just hit the "Print Screen" key, then open Photoshop, select "create new canvas" and then select "Paste" (or hit CTRL-V) anywhere on the new canvas. The entire contents of my Windows screen magically appears. Crop it, save it, and be done with it.
In this particular case, since I knew I was posting it on CPF, I decreased my browser window's width *before* taking the screen dump (yes, that's what it's called! :0) so it would fit on most people's screens without causing the topic to scroll horizontally.
No Photoshop?
Then after you've grabbed your screen, just open Paint, and hit CTRL-V anywhere in the blank area. A thingie will chime in saying the image on the clipboard is larger than the canvas; just answer "y" to whatever it asks, and presto. Select Save, choose the format of your choice, and that's it.
I don't know how to crop images in Paint, so my usefullness to you in this situation ends here.
For a screen with a lot of blank space on it like the web shot above, I convert it to GIF so the text would't degrade and start bleeding into the background like it will if you save it as a JPG with high compression. For a photo you grabbed this way (such as from web pages that have Right Click--->Save As disabled), save the screenshot or the cropped screenshot as a JPG or other 24-bit extension of your preference to preserve the color depth. (Web-friendly formats are .GIF and .JPG)