What one song would you recommend I download?

I'll unashamedly admit I stole this idea from another blog.  And I'll also admit my motives are a bit selfish, but I suspect all of you have exquisite musical taste.  

So here's the question:  if you could tell me to download only one song, what would it be and why?  (Please don't say "because I like it!")

You may be asking, "What does this have to do with parents and teens?"  I'm hoping it will encourage parents to listen to some of the teen suggestions and vice versa.  

At the very least, we can all expand our music library.  And hopefully our minds as well.  :)