On EFL Classroom's Karaoke page, you can download hundreds of premade karaoke files.
Also, there are many more places to get karaoke videos and learn about karaoke:
1. Discussions about Karaoke
2. Main Karaoke page
3. Karaoke video examples
4. Quick Karaoke
5. Kids Karaoke Korner
6. News articles in Karaoke
7. Elementary Songs for the Korean Textbook
8. Mixtube lyrics/songs
9. Go Sing player and songs
10. Karaoke in the classroom group 11. Karaoke Videos on EFL Classroom 2.0
12. Karaoke Dialogues