Every now and then, I put remixes that I call remixapellas on my mix cds. Remixapellas are simply what the words says; remixes with acapellas. Essentially, I take the acapella (just the words) of one songs and blend it with the instrumental of another song. First, I make sure the tempo of each song matches and then I determine whether or not the two songs make sense. Lastly and most importantly, I make sure that the pitches of the vocals and instrumental both match. By doing all of these steps, you give the listener the perception that the songs is a new song that he or she has never heard before.
Attached is a mix that I did back in '05 when I was living in Little Rock, AR.