This is one way I've found to work well for precisely syncing audio recorded on a separate system. In this case, I recorded the audio on the Zoom H1 and the video with the Canon T2i.

As I watch this screencast I'm sure someone is going to ask how I got the Zoom H1 to record a mono lav mic input into stereo sound -- don't worry, I didn't. I used the batch export command from the File menu in FCP to export the files after centering the pan of the left channel...at least I think that's what I did. It was late and the details are fuzzy. ;-)

The key to this method is getting the audio matched at the sub-frame level (1/100 of a frame) so that everything is perfectly in sync.

I used a home made slate I made with a piece of scrap wood, a hinge, an 8x10 picture frame glass and some mirror holding mounts. Finished it off with a paint job using some spray paint I had on hand.