My pediatrician told me the fours are worse than the terrible twos. At four they know what they want, but lack the tools to use that knowledge for good and not evil. ;)
When my son went through the defiant stage, I tried everything to get him to be respectful and cooperative. Spanking did not do any good either. Then my mom told me how she worked through MY defiance. (She also laughed and said I was getting paid back but good, but that is another story) Anyway, she said you have to find what toys or activities or priviledges matter to your kid and use them to make an impact. For my son, if he was defiant, he lost his computer use for the day. If he lost his computer and still sassed me or ignored me, he didn't get to watch Spongebob. If that didn't stop it, he went to bed early. Usually he didn't go past the computer loss. But you only give one warning...say, "If you don't pick your toys up and I have to remind you again, you lose ________ AND you will have to pick up your toys."
Good luck, and be of good cheer....it passes. My son now is five and is just a thoughtful, respectful, sensitive kid.