I had the same "I'm not tired" strop from my lad yesterday when he failed dismally to do his maths homework properly - I'd found him the night before at 10.45 watching a DVD in his bedroom. He's on a one more chance & the TV/DVD combo go.
He's also got a Ipod Touch, but got TBH I'd not considered what time he might be using that to. Might just turn off the router this evening and see if he complains.
If he wants his internet access back, then make him earn it by regaining your trust etc. Easy way to do it is to let him have internet access when he is in the public areas of the house, and not in the privacy of his own bedroom. Let him keep contact with his friends socially, without taking the piss late at night. Eventually you'll all move on, he'll restart late night surfing sessions on his Touch mostly because you'll forget to switch the router off one night!
My lad is late primary school age, but I'm unkeen on him using laptop etc in his bedroom - whatever he is looking at online at his age should be fine to be looked at in the comfort & company of his parents in the living room. Agree, it gets harder with teenagers, but they're also perhaps more vulnerable to online approaches sometimes.