I've tried a bunch of tools. Pearlyrics is gone thanks to the RIAA, it was great because it would go through your whole set of songs. All the rest just do the current playing song and most are widgets now:
# "Harmonic:http://www.macupdate.com/info.php/id/2035. This seems to work the best. Listens to the current song and plugs the lyrics into iTunes and therefore into the MP3s.
# Cantopod. Nicest interface, but doesn't automatically insert
# I Sing iTunes. This is most popular sing it handles Japanese and Chinese lyrics, but it seems to hang for me.
# "Album Art Thingy 1.9":http://www.apple.com/downloads/macosx/ipod_itunes/albumartthingy.html. Reported downloads artwork and lyrics inthe background. Cost $15, but saves lots of time!
# "Amazon Album Art Widget":http://www.versiontracker.com/php/dlpage.php?id=28644&db=mac&pid=85611&kind=&lnk=http%3A%2F%2Fwww.widget-foundry.com%2Fdownloads%2FAmazonAlbumArt-2.12.zip is a manual utility and looks up the current song.
# "GimmeSomeTune":http://mac.blorge.com/2007/10/21/free-mac-software-sunday-automatically-fetch-itunes-album-art-with-gimmesometune/ is donationware that does lyrics and artwork.
Also you want to automatically get artwork. ITunes finds artwork, but unless you manually go a Get Info and put it in, it doesn't copy it into the MP3.