What's the best way to tell your boss that you want to resign?

Face to face is always the best way. By using a letter, it looks like you can't face him. Whatever the reason is, you can face him. It is your life. He is living the life he chooses and you should, too. What you should say depends on the reason you are resigning. It is always nice to include with whatever you say that you appreciated him hiring you and you have enjoyed working for him.

To me, one should be straight in his doings. so in normal circumstances , he just send the resignation to his boss and then wait to see his Boss's reply. HOwever this can be different in other scenerios . For example, you can give a hint to boss of your resignation etc. It depends upon the situation.

I would write something to the effect of (if it is true) - that you have enjoyed your experience working with the company, that the people were wonderful etc, but you found yourself wanting to move on to expand your career or change careers and you gave it serious thought but what you wanted to do was not available in the company at this time (leave your options open in case you want to come back in the future). You appreciate what you have learned etc and would like to remain on good terms with the company. And should the time come when you working for them again would be mutually beneficial you would like to be considered for such opportunities. (THis is way to much thinking to be done for between shifts. SOrry - 1/2 asleep and posted as comment earlier.

If my boss is not very close to me, I'll just type a resignation letter and put it in his office..and then wait for him to call me in. If he is close to me, I'll 'discuss' with him about my decision before doing anything. I had a boss who's rather close to me. After 'resigning' for the 3rd time, I manage to leave the company coz his contract in Singapore ended and i took the opportunity to move on.