I've really been enjoying listening to Pandora lately.  It is a net radio service that builds a "station" for you based on your tastes.  You begin by entering a song or an artist you like.  It then plays music it thinks is similar.  You are allowed to give the selections a thumbs up or thumbs down.  Based on your input, it refines the programming.  This is a great way to discover new music.  Today I started with Evanescence and discovered Leaves' Eyes and Nightwish.  Now if someone just would just make a full-featured Pandora module for Media Center...