DoubleTwist is a solid product and it just got better. DoubleTwist now features an integrated music store powered by Amazon’s MP3 store. The interface is simple and much more straight forward than iTunes. The only downside is that it doesn’t appear to have album charts or genre categories.
I’ve been passively watching DoubleTwist for a while now and although I wouldn’t consider using it myself (because of my iPhone) I would suggest it to anyone who wants an iTunes-like interface for syncing any non-Apple device.
Update 10/20/09: DoubleTwist has announced that the software now syncs with the iPhone and iPod touch. They are currently only supported with the Windows version, but it shows promise.