The Xbox 360 S has a cool little latch you open to find the slide-in hard drive port. Say you got one of those weakass 4GB systems and now you're finding you need more storage. You can now nab the 250GB drive for your system at Gamestop, as they've been made available for sale for the first time.
I ran a search to see if the drive is in any of my local stores. No luck. But it seems that there's some in east and west coast stores.
F0r $129 you get the drive and three demos: A Kingdom for Kefflings, Peggle and Pinball FX.