A brand new demo is out on the marketplace. Amped 3, which has been out since the console release, has finally released a demo out on the Xbox Live Marketplace. The demo is 767 MBs and can be found in "Demos & Trailers" section of XBLM.
I played the demo for a bit last night, and I think it is one of the better demos that is available in the Marketplace. The basic goal is to get 50 people to be impressed with your moves. Pull of longer and more combos, the higher your meter fills.
Also themes and gamer pictures are also available for Amped 3. They have been out for some time now, but the theme is 150 points and the 10 gamerpics are 20 points each.
–backdraft123
BD's Bodacious Blog 
I was actually doing an entry about this demo this morning at around 2 AM when I realized that this demo just didn\’t deserve it. I will try and play more into it later, but most of the challenges are too easy, the graphics are just like Amped 2 HD, and the gameplay just does not fit my fantasy style. The theme looks very nice, though.- Go get that Webby!