Ok... here we go.
The key is not to get nervous, especially on a green horse. So I know it might be hard at first to think about letting the reins loose, but trust me, it will help out in the long run, and he will be a lot easier to ride. So... Loosen your reins!
Start out cantering straight on the rail or in a large circle. Then, slowly release your reins more. It obviously doesn't have to be a huge drape, just enough that there is actually visible slack in the reins. Now as soon as you feel him speed up without you asking (which will probably be instantly the first few times), start the spiral... which is just like what it is. Pretend there are lines on the ground creating a spiral. Start out in a big circle, then every time you go around, make the circle just slightly smaller. Do this until he is going into the smallest circle you are comfortable with, or that he will do without breaking gait (don't let him). When you have come to the center of your spiral, slowly work your way out again, making the circle slightly larger every time you go around. Eventually, you can go back to the rail and try again. Enough spirals will cure the problem. lol. And it is also great for getting them to work their hind end if they tend to be more heavy on the forehand.
As for the head tossing, I see 2 huge problems...
1. He needs to get his teeth floated asap.
and 2. (which I believe is the biggest problem) Is the bit.
It is only my opinion, but I HATE Tom Thumbs. And it amazes me how many people use them. I used to do mobile training, and almost every owner stuck one of those bits in their horse's mouth. It's like... "No wonder you have having problems with him/her..." Then I tell/show them how every time you stop or turn using direct pressure, it stabs their horse in the roof of their mouth. That seems to make them flinch and understand very quickly. And then I put a plain 'ol snaffle in the horse's mouth and the watch me get the horse do everything perfectly.
Sorry... Kind of went on a tangent there... I really, really dislike those bits. I believe almost every horse can work in a snaffle, at least in the arena.
So... You know what I'm going to say next as a response to your "which bit should I use?" question... lol. A snaffle! I personally love the western-style dee ring snaffles with a sweet iron mouth and copper inlay like this... Kelly Western Riding Horse D Ring Snaffle Bit - eBay (item 390089587207 end time Sep-09-09 15:07:57 PDT)
You almost HAVE to be riding in a snaffle to do things like spirals, you will be direct reining, and you just don't get the same flexion/feel with a curb or shanked bit. But if you really need something with a shank to keep you comfortable, get something with a short shank, still with a broken mouth. Like an argentine snaffle... NEW ! Argentine Copper Wrapped Snaffle Bit with silver - eBay (item 350250058222 end time Sep-10-09 19:25:15 PDT)
I hoped this helped! And let me know if you have any questions or if he won't slow down, I have a few other things you could do. =]