Music video clips are great, but storing them and also the MP3 is not the best way of doing things. This is where Stereoclip comes in and it will synchronize whatever you're playing through iTunes with videos of the playing track through YouTube.
It's powered via Adobe Air and is a free download for OSX and Windows. When the app is running, it will play a YouTube clip of any song you're playing through iTunes, synchronizing the time of the song to the time of the video. If YouTube doesn't have an official video for that song - such as rare music selections or live tracks, the app will find live versions of people singing/playing the song in their bedrooms.
Visit Stereoclip's website by clicking here.