No one does racing music like Nintendo. Hell, music in general. There's a shine and polish on their work that no one else touches, and the melodies stick with you forever. As expected, Mario Kart 8's soundtrack is outstanding -- it's so good that I'm willing to put up with terrible YouTube commercials to listen to it.
YouTube user vini64 has created a playlist of the entire Mario Kart 8 soundtrack for your listening pleasure. I'd recommend streaming it all if you have the kind of job that has you sitting at a computer all day, as it's ideal background music. The soundtrack sparkles with live performances, solo highlights (fiddles, guitars, synths), and lots of fun callbacks for series fans. I'm so happy. You will be too.
If you're short on time and want just the highlights, here are my favorites so far: