Five Details has Seamless (iTunes Link) for the iPhone and iPod Touch in the iTunes App Store for FREE (regularly $1.99) for a limited time.

With one tap, Seamless fades your music, podcast, or audiobook out on your Mac, and in on your iPhone (or vice-versa). When you’re ready to transition music from iTunes to iPod, tap Seamless on your phone, and boom. The music fades out on the Mac, and fades in on the phone. Seamless requires a companion mac app, which is also Free.