So Xbox is doing a Mass Effect promotion where people have a chance at winning early access to the Mass Effect 3 Demo, or the Normandy Avatar Prop.
It's a Facebook App, so you'll need a Facebook account. Then you need to load this app: https://apps.facebook.com/xboxmasseffect/
Click 'Launch' and a pseudo-game will launch. What you have to do is press 4 buttons in any order. That's all you have to do.
While it may seem that you need to press them in a certain order, you do not, it is entirely random. If you're lucky you will win a code for either the ME3 Demo, or the Avatar prop.
Once you have your code, redeem it here: https://live.xbox.com/redeemtoken
This is an Xbox 360 only thing, so you'll have to be a 360 player. If you don't have an Xbox but do have a Facebook account, why not be generous and give it a go and share any spoils with your fellow wiki editors, or one of the thousands scrambling for a code over on BioWare Social.
They were going pretty frequently earlier, but it seems the frequency of winning has decreased. I myself had to try 17 times (3 attempts per Facebook account every 2 hours) with 3 dummy Facebook accounts before I got anything. Generous BioWare Social users are also posting spare codes in the thread I linked to above if you want to give that a go. Apparently there are 10,000 codes up for grabs, and there can't be many left, so what are you waiting for!?
Good Luck!