T.,
You could be talking about my 4 1/2 year old son. I too had tried everything, and had finally given up and did my own post (More Potty Training Woes). The advice that has worked for me were:
1) Set up a calendar that he gets a smiley face and sticker for everyday he's clean and dry. At the end of 10 consecutive days he gets to ride on the Edmonds/Kingston ferry to get ice cream.
2) When he has an accident he has to clean it up in the bathtub with the coldest water I can get out of the tap.
3) Because of the monsters in our toilet that try to get him, he gets the choice of either sitting on the toilet, or squatting so he can see below him and make sure the monsters don't get him. ;-) (I only figured that one out after talking with him during dinner)
4) He goes when he wakes up in the morning, before we leave the house, when we get where we're going (long trips usually), before we leave where we're at, after meals (usually about 30 minutes later), and before bed.
So far it's worked well. We still have accidents, usually peeing in his pants. But he has gone 6 1/2 days accident free.
Hope this helps,
Melissa