This website called LyTube puts karaoke, sing-along style lyrics on top of any video you plug into the site. Simply copy and paste the YouTube link into LyTube. I tried it out with "Just Like Heaven" ...

You're out with friends at karaoke. Your turn is next. But dang, you still don't know what song to sing, and you're not a great singer. What's more, someone just nailed "You Oughta Know" by Alanis ...