X.O.
Is he still taking a daytime nap? If so, you might need to drop it, shorten it, or find ways to tire him out after his nap so that he'll be tired enough at bedtime. (We've been going through the same this with my 3 yr old).
ETA: We've been taking after-dinner walks and trips to the park. Instead of just letting them play on the playground, I've been bringing some balls and we run around in the field for a LONG time. By the time it is done all the kids are toast and ready for bath & bed. Very rare that they resist bedtime after I've run them ragged.