To get good sound, we must do what the professionals do, and record our sound seperately, and with reasonably priced, high quality recorders like the Zoom H1 (much beloved by indie film makers) available, there's no reason not to.
Seperate recording however, does leave the problem of how to match the two files together afterwards? So, in this video, I take a video clip, and an audio recording from a Zoom H1 recorder and show how to synchronise them together in post production.
It's not complicated or difficult at all, but the difference in sound quality is very impressive - Try it yourself.