Scrivener asked about the Lips game, and I was really late in getting back to him in the comments, so I thought I'd cheat and make a quick post out of my answer.
I like Lips a whole lot, and one of the really nice things about it is that you can add your own songs (unDRMed MP3s only, I think) to it, but it's not as seamless as you might hope. You don't get any lyrics or pitch targets with your own music. I don't care too much, because I just pop the lyrics up on my laptop, and I don't care too much about the pitch targets. The other downside is that they're releasing new songs every Friday (or thereabouts) which might sound really great, but each song is another purchase. They run about $2/song, but that gets you the song, the video, the lyrics and the pitch targets. I still don't know how I feel about all that, but I've bought several already.