A Gold Members exclusive SSX demo is now available on Xbox LIVE Marketplace, measuring in at 1.24Gb.
The demo will also be arriving on PSN tomorrow, when the EU Store update arrives. In the meantime if you have a Xbox 360 you can add the demo to your queue here.
SSX is due to launch on March 2 on PlayStation 3 and Xbox 360. You can pre-order your copy here (PS3) and here (Xbox 360).