The new Genius playlist feature in iTunes is brilliant. Click on a key song and it will generate a playlist. I've tried this a few times and it's worked amazingly - Adele's "Chasing Pavements" generated not just a Kate Bush song, but the perfect Kate Bush song ("This Woman's Work.") It went like this for everything I've tried. With a large iTunes collection, it's like a better Pandora, or even more like the most perfectly selected satellite radio station. To me, this is the most revolutionary digital music innovation since iTunes/iPod iteself.
Here's an example for Bettie Serveert's "Tomboy"
