The majority of lyrics I've downloaded so far comes from
http://leoslyrics.com/. Its database is impressively big, lyrics are still being added regularly, and the site has existed for around 3 till 4 years now.
The Winamp plugin available on the site allows you to download lyrics automatically, exporting them afterwards makes the lyrics available for other programs without having to manually rename the text files generated by leoslyrics. Besides, in conjunction with Winamp's
Intro Play Plugin the downloading can be done overnight.