Potty training ideas for a boy?

My son is almost three and wont potty train. I've tried stickers, books, gummy bears, putting him in underwear and letting him pee, but he wont sit on the potty. He cries everytime I mention it. I don't want to force him kicking and screaming to do it and make it a bad experience, but I really need him trained. Anyone have any good suggestions that has worked for you?