FreeKaraokeMusic posted a big archive of MIDI karaoke tracks and I got it today. Thousands of songs, and since it’s all MIDI, the files are tiny and you can download it in just a few minutes.
People have been posting MIDI to the internet since the dawn of geocities, I don’t think there are even any copyright issues here.
Click here to download: http://www.megaupload.com/?d=EXW9F5OD
There’s even some Latin and Brazilian stuff here too!