Create your own games for Xbox 360

Microsoft announced that they are making XNA Game Studio Express, a program that helps you create games for Windows and the Xbox 360. A free beta will be available August 30th for Windows. The full version will be released around the holidays, and while free for Windows there will be a $99 annual fee to share and play games on the Xbox 360.
Here's where you can go for more info:
Let's Kill Dave - a list of links to different articles about it
Gamerscore Blog - a good overview
Joystiq - a good write up on what it is
Joystiq - how Sony tried (and failed) at this before, and how Microsoft can do better
Xbox-Scene - The most interesting FAQs, and a description of how it will work with the 360
XNA Team Blog
XNA FAQ