Do you have video files that you'd like to have in audio form—say a music video you bought from the iTunes Store that you want to listen to on your iPod? Reader sabberworm has pointed out a nice hidden feature in iTunes that lets you do just that. He uses it to grab audio from video podcasts, but you can use it to save the sound from any video file as an iTunes track.
If you select a video in your iTunes library—this could be a music video, TV show, or concert video—and look in the Advanced menu, the Create AAC Version menu command is dimmed. (The format might be MP3 or Apple Lossless, depending on your import settings in iTunes' General preferences.) But if you press the Option key, this menu item changes to Convert to AAC (or, again, MP3 or Apple Lossless, depending on your settings). Select that command, and iTunes will happily rip the audio from the video.
I've written before about ripping audio tracks from DVDs, using Handbrake as a middle-man. But if you already have the videos, you can get their audio with iTunes using this menu item, as long as the video is in an iTunes-compatible format (.mov or .mp4).
Depending on what you want to do with this audio, you may want to use your default iTunes settings, or you may want to rip to Apple Lossless. Just remember that the audio quality will be no better than the original video's.