Tunescape passed peer review earlier today and is now available on Xbox Live Indie Games for 80 Microsoft points ($1). I know, pretty spendy...
Last time I checked, it was not yet showing up in the "New Arrivals" section, but if you search for it under 'T', you can find it.
The Tunescape page on the web-based marketplace is here.
I've also put together a little promo website: