Movie Sync

Movie Sync allows you synchronize audio and video in QuickTime movies. You can also synchronize other QuickTime readable media, such as AVIs, MPEG-4, and, with appropriate codecs, even WMVs.

(Results are always saved as a QuickTime movie; MPEG-1 and 2 cannot be synchronized at this time.)

Movie Sync has been designed to be incredibly easy to use.
Open a movie.
Play the movie. (It is usually best to begin where synchronization is worst, which is often near the end of the movie.) When you see & hear a spot where the audio and video are out of sync, hit return. The portion of the movie just played will loop over and over again.
Use the arrow keys on your keyboard to adjust the audio until it is in sync.
Hit return to accept the sync point.
Find a few more points to synchronize.
When you are satisfied, choose “Save As…” from the file menu to save a new new, synchronized, QuickTime movie. Don't delete your old movie, just in case!

If you have a mouse with a scroll wheel, you can use that for an even easier experience!