Bert was following these instructions to make an iPhone stand out of business cards, and was less than satisfied with the results. After staring at my own phone charging on the desk, I figured that the dock cable connection would be a useful mounting point for any stand. Bert dared me to make a stand with only office supplies, and a few minutes later I had a fully functional stand using nothing but a medium binder clip.
Just clip a medium binder clip over the plug, tip the iPhone back and bend the rear hinge of the clip until it balances naturally. The dock cable is an integral part of the balancing system; make sure the cable is lying flat to help weigh the iPhone down or it will topple over helplessly. To remove the iPhone, simply unclip the binder clip and unplug the phone.
I happen to use one of the old "fat" charging cables that came with my now-deceased 2nd generation iPod. The new ultracompact dock connector cables also work, but I find the binder clip to be a little wobbly because it has less of a purchase on the smaller plug. However, you can easily make it more sturdy by clipping a small binder clip onto the cable first, giving the medium binder clip more surface to sink its teeth into. This configuration has the advantage of allowing quick release; the old dock connectors have locking tabs on either end that you need to squeeze to disconnect, so you need to remove the binder clip before unplugging. The newer dock connector cables can be yanked right out.