If you have a long and heavy lens this might help you. I got it for my Tamron 400 and it feels much lighter with it since the lens rests on your palm rather than your fingers, focusing is easier and it is more stable, too.
You need a door knob, a plastic washer and a screw with course thread (I don't remember the diameter- sorry). Saw the head of the screw off, and wrap it with scotch tape that it just fits in the hole of the door knob, fix it with the screws on the knob. Get the shortest knob you can find, the one I used in the picture is quite long, I would prefer it about 1cm shorter.