Has anyone ever used a camcorder with an external microphone?
Yes, there are several mics available that generally produce much better audio than the "built in" mic.
I was wondering if was possible to use a regular vocal mike using some kind of an adapter to plug into the camcorder?
Some, not all, camcorders have a 1/8 mic input that you add a external mic to and will definitely enhance your audio recording. Good mics will run ya $150-200 though!
A dynamic won't work well, use a condenser designed for that type of application as Mark suggested. You can also use recorders like the Zoom H4n and then sync the audio with video using software.