I have a method I use that works better than any other I've tried, but it comes with risks. Supercropping! It basically amounts to bending the shit out of the main stalk-practically breaking it. If you do it right, then the main stem will stay bent at a 90 degree angle for a while, then the top will start growing vertical again. I've taken a 3' plant and reduced the height to 2' using this method. The risk is that you can kill the top if you do it wrong, and sometimes the 90 degree bend will just stand right back up and heal itself. The end result is a shorter plant, you keep your top, and the lower branches get stimulated to go crazy.
Topping does work also-promotes branching and all that but you have to cut off your beautiful top to do it. I'll post some pics of what mine look like in a bit-gonna eat some lunch now...