MusixMatch has collected the lyrics to more than 5.6 million songs from more than 500,000 artists. You can comb through the lyrics by artist, album, or track. All of the songs are licensed with the major companies, thereby avoiding copyright issues.
MusixMatch offers an API with basic searching, as well as a PHP library, an Android plugin, Perl, Ruby, and more. Prices begin at $1.40 per 1,000 views on a mobile device and rise from there.