Neon, the music visualizer from Jeff Minter absolutely rocks! It totally blows away anthing I've used on PC or XBMC. It is not only gorgeous in motion but you can control it in real time with the analog sticks. A lot of fun! (I spent a lot of time just playing with it tonight)
Hopefully the live features are enabled for the 360 soon. I was able to transfer my account so you should be able to see what I'm playing under Spudzspot
I really can't wait to see that feature running.