What do these songs all have in common?

I created an online mixtape, on one of the most graphically sleek sites I’ve seen in a long while [muxtape].

You can hear it by clicking below. For bonus points, try to figure out the common thread which binds these songs together.

Update: Many people also swear by mixwit, which has a nice interface too. And you can make multiple mix tapes.

Update: Answer to the question in the subject line in the comments.