In addition, there will be many add-ons. For $100, you can buy the 20GB hard drive. For $40 you can get a 64MB memory unit. For $50, you can get a wireless controller. For $20 you can get the Play and Charge kit for your wireless controller, pending that you have rechargable batteries. For $12 you can get a rechargable battery pack. For $100 you can get a wireless network adapter. For $20 you can get a headset. For $30 you can get the media remote. For $30 and $40 respectively, you can get S-Video cables or HD AV cables.
Phew, that's a lot of add-ons. Here's the deal: you'll want to get the $400 kit and then buy the $50 wireless controller. So, you're looking at $450 to get set up the way you should be. If you're not a hardcore gamer, the base model will work fine and you can always add on later.
No word yet on the release date, but it is only a few months away and the announcement, I bet, is coming soon. We'll keep you updated.