ITunes Lyrics Importer
ITunes can display song lyrics for music files, but it doesn't automatically slurp in that data as it can album art. To do that, grab the free iTunes Lyrics Importer. Close iTunes first, and then install and launch Lyrics Importer.
You can obtain lyrics for specific tunes by selecting one or many songs, and then clicking the Get Lyrics button. Preview the details if you want, and then click Update. You can also update your full library in one swipe, without verifying each track.
IPod Lyrics Importer stores the lyrics within the song file. To see them and sing along, right-click a track, select Get Info, and choose the Lyrics tab to sing along. On an iPod, press the center button several times to cycle to the lyrics screen. On an iPhone or iPod Touch, just tap the screen while playing the song.
Note: This link takes you to the vendor's site, where you can download the latest version of the software.