I personally recommend joining a local Toastmasters club. They can help you with speed, tone, volume, etc. It can benefit your conversational speech as well, not only public speaking.
Or a local speech course. I took an eight-week course in public speaking in college, and it was probably the most useful course I took there. I can do talks in front of tech groups or hobby groups... not without some sweating, but still more effectively than most people.
