Sad to hear that the reward system doesn't work -- I had lots of problems with my 3-yr-old where his bedtimes were turning into an ordeal for everyone. Decided to use a sticker chart, and within a couple of weeks the whole situation had totally resolved and everything was fine.
What we did was to give him a sticker every time he went to sleep 'like a big boy' and then, any time he got three stickers in a row, he would get a 'treat' (anything from a delicious dessert to a trip to the cinema or just a new book or something like that -- keeping it vague and changing it up all the time kept the whole thing fun and kept him guessing and curious to see what the next treat would be.)
Anyway, that's my only advice. It sounds like you've tried everything else!
