Some of you may have already known this little trick but I just discovered it tonight. Put your lens in manual focus mode and then while adjusting the focus ring hold the shutter button down half way. When the image is in focus the viewfinder on your 7D will flash red and you'll hear the focus confirmation beeps.
I'm not sure if this tip works for all Canon cameras but it certainly did on my 7D. If you try it with a different model and it works how about letting me know.