With this free iPhone app and effect plug-in for PC and Mac you can easily remove vocals from songs!
Vocalzap is a free iPhone/iPod app that can effortlessly remove the vocals from any song. If you want to sing along, click the "Lyrics" button. Toggle between the original singer or no vocals with the click of a button.
Remove vocals from most song
Look up lyrics to most songs (iPhone only)
Toggle between vocals and no vocals to compare
Use it for Karaoke parties with your own tunes!
Note: Does not work in iOS7