Be consistent :) I have a strong willed boy too so I had to respond, if anything just to say you have my support and understanding! Mark, my son, is VERY strong willed - but we've managed to get him to understand what time out means. And he gets his share of spankings as well - we make the punishment fit the crime, but most of the time, it's a time out that upsets him the most. Also, here is an idea. Try taking away something that is important to me, if it relates to what he has done wrong...like a favorite toy, telling him he can't play with it for a few days, or some special time, removing that. Also, imo, although he goes stiff when you try to hold him in the chair for time out, you just have to be consistent with it. You have to win the battle - that's important. And choose your battles wisely :) I learned that early on. So, if you want him to learn to sit still in that chair, you'll have to make him sit there until he learns you aren't backing down. If you back down just once, he'll know that you'll eventually give in if he fights long and hard enough.
Just my thoughts - I've learned alot and struggled with this, still struggling and still learning - it's a rocky road but oh so worth it...such is being a parent :)
Oh - far as books. My favorite discipline authors are James Dobson and Kevin Leman. I also liked a book I just recently read called Be the Parent, by Kendra Smiley.
R.