Combine sound such as MP3 to video MOV in OS X?
iMovie is the obvious choice. It's very easy to use and fairly reasonable in price. You might have it already if you have a newish mac or else it's $15 I think.
http://www.apple.com/ilife/imovie/
ffmpeg supports combining video and audio without re-encoding:
ffmpeg -i input.mov -i input.mp3 -c copy -map 0:0 -map 1:0 -shortest output.mov
-map 0:0 means input file 0, stream 0. -c copy copies video and audio codecs. -shortest makes the combined file as long as the shorter file.