Nike's C.O.R.E. Audio iPod Backpack won't track your workout data like the Nike + sport kit, but it does have a "padded media pocket" with a dock connector for iPod stowage and an integrated remote control keypad on the strap that allows you to conveniently control your music (play/pause, change tracks and volume). Apparently it's been available in Europe for a month or so, but there's no sign of it on the US Nike website yet - although a Google search did reveal it being sold by many online retailers selling it for $85-$100 USD. At roughly half the current price of the Burton Amp iPod Backpack (which was even more when it was introduced), that seems like a good deal. Personally, I found the Burton backpack to be uncomfortable for every-day use when toting lots of gear, so I might give the Nike Core Audio version a try.
The backpack features ergo-friendly straps, a padded laptop compartment and a convenient earbud storage pouch. The built-in 30-pin dock connector is compatible with 4th generation iPods, the iPod mini, iPod nano, iPod photo and iPod with video.
iPod-fun.de has a few more pics if you're interested.