What sort of footage are you shooting?
high def, (xa10 canon) cabaret performance....if i understand what you are asking......
I sync multiple video and non-sync audio all the time. It really helps if there is a clap or other distinct noise recorded on all the devices at the same time. Then you can identify it with a marker in the source window on each clip and either let the mulitclip create a multiclip sequence (if you plan to edit multicam) or just bring each one into the timeline on its own track.
If you don't have a clap recorded start with the shortest source (assuming they all recorded everything). Find the first instance of a word like "hello and welcome to..." and mark the "he" sound. You will have to really really zoom in to the audio waveform. Do the same with the other sources.
It's mostly a matter of practice and, of course, ensuring that all the sources are rolling all the time. Don't stop for anything! You could invest in a product like "Plural Eyes" but really, it's not a difficult art to perfect.
I have built a small tone generator that will give out a beep when a button is pressed, the sound man feeds this to all my cameras and his audio recorder. This does not disturb the performance as no one hears it, unlike a clapper. It is then easy to align these beeps on the timeline. I often use different number of beeps to identify different songs or acts. As Allynn rightly said keep everything rolling for as long as possible. For aligning just video, still camera flashes are useful.