How do I add lyrics to a song in iTunes?
I own iClip Lyrics and I was fortunate enough to download it before they discontinued it.
(It still works even though they aren't developing it, and if you can find it online I highly recommend it)

All you had to do was play a song, it would search the internet, grab the lyrics, and automatically add them to the ID3 tag for the the MP3 file.

There are some other apps out there that do basically the same thing:


GimmieSomeTune
TuneLyrics
iLyrics