Any success with external microphones for Android phones or tablets? What's the best way to record a video with high quality audio?  Specifically, this is for a presentation where a microphone could be placed by the speaker.  I know that an app that records with the right codec is necessary, but what about the microphone?

I'd prefer to use a USB mic but, even though Android 3.1+ supports USB host mode, it doesn't appear that this is easy to accomplish.  What about a 3.5mm microphone - would that yield acceptable results, or would it be better to stick with the built-in microphone?  Are any of the video-recording apps capable of handling the microphone?
It's not a USB mic, but I have found a solution for external mic via 3.5 mm jack.

Look at my answer on this question: 
How do I use an external microphone with my Galaxy Nexus?