What are the things that he really likes? Whatever it is, the Gameboy or a game system or TV time or going skateboarding....crack down *now*. Revoke the privilege, having sat down beforehand and telling him that this lying is not acceptable and that there will be consequences. Make sure that Dad is on board with all this as well.
And then when he lies again, the skateboard(or game system or whatever) goes *away*, in some fashion. The "taking away TV time" for every fib is a great idea. Maybe give him a certain amount of TV time at the beginning of the week. Then for every lie, "Sorry, that's 30 minutes less!" Stick to it and he'll get the message. If you think it's appropriate, he could perhaps earn his privilege back by doing extra chores, like cleaning the tub or toilet

.
Or if the whopper is a really big one, where someone could have gotten hurt or he lies about where he's going after school, etc....You could even decide to give it away for keeps.
You have to (metaphorically) hit him where he thinks. Whatever that special something is, take it away. Does he have a TV in his room? It is gone. Is he planning on going out with some friends? Sorry, he can't go, he's on "restriction".
An occasional fib is not a problem to me, but I would have a problem if my DD, for instance, started lying about every. single. thing. How would I be able to trust her with responsibilities if she lied all the time?
Good luck. Parenting is the hardest job in the world.
agnes!