Most riders don't realize it but guess where most head-shake originates? The obvious answer is in your head, but the main cause can usually be found at the other end of your bike... In the rear shock. If the suspension is not balanced, all sort of weird things can happen. If you have too much rear sag, the back of the bike is riding lower (because you let too much weight transfer to the rear wheel) and actually pushes up on the front end and makes it lighter and more vulnerable to head shake. Set your rear sag between 90 mm to 100mm depending on the type of riding you do. Bet that pesky head shake goes away. If you haven't done so, talk to a susp. tuner about proper set up.
Personally, I feel that one of your best hop-ups is a dialed in suspension. Most riders talk about pipes, rad valves, jetting and big bore kits to make their bikes faster but in truth these riders don't use the power a well tuned stock bike has to offer. I'd go for correct suspension set up over any other hop up. (One example is head shake. It tends to cause one to let up on the gas when it happens.)
Hope this helps!!!