Lyrics Plugin is a free software that shows lyrics of songs in Winamp and Windows Media Player. Whenever you play songs in Winamp or Windows Media Player, Lyrics Plugin connects to online database, and fetches the lyrics of song being played. It then displays those lyrics.
Lyrics Plugin reminds me of Tubeoke that lets you see lyrics of Youtube videos.
If Lyrics Plugin works off a pretty huge online database of Lyrics. However, if it is not able to find some lyrics, it lets you provide those, which are added to the database too.