Requires iOS 4.0 or higher.
With SwitcherLyrics you can have your song's lyrics and information right in your Multitasking bar. You just have to double tap the Home button to make it works. SwitcherLyrics takes the song's lyrics from iPod.app's library.
If iPod.app doesn't have any lyrics, SwitcherLyrics will search it on the web automatically.

See the Screenshots below for a preview.