I have found a new position and need to let my current company know. What is the most professional way to tell your boss that you are quitting? Is it via email, in person, or something else? Is there anything I should consider when making the choice?
Unless you're a telecommuter and telling your boss in-person involves getting on a plane, tell him/her in person. It's awkward and uncomfortable, sure. But some things you just have to do. Have your resignation letter with you, and hand it to your boss after you've said your piece. It should mention the effective date of your resignation and/or what your last day on the job should be.
Before you meet with your boss, you should at least think through how you will respond to, say, a counter-offer, or what you'll do if your boss gets angry or unreasonable (if he/she has that kind of personality).
Always in person, unless circumstances don't allow. If you can't do it face to face, choose the most personal method possible - that will usually be by telephone, but don't do it by leaving a voicemail message.
For example, when I resigned my last position, the manager I reported to was located in another city a couple hundred miles away. So I had to call him. We played phone tag for the better part of a day before I could finally get him on the phone to tell him.
Once you've told your manager, follow up in writing and explicitly restate your final date. Be sure to offer to help with the transition.
In person would be best as there may be changes in the terms of your departure. There may be questions from your boss that are best discussed in private face to face. There could be questions about how your work will be re-assigned, what the timeline is and a few other things that could be discussed here.
Do you ever want to work with this place again in the future? Think there's a chance you'll run into this person again?
Just do it face-to-face. No reason to scorch the earth on your way out. You never know who will run into who or how things will play out in the future. I still chat and keep tabs with two previous bosses from over the years because of how I handled my exit strategy.