MS has another holiday promotion, but this one is UK only. If you have an XBOX 360 and someone you know buys one between Oct. 1st and December 14th, both you and the friend are eligible to receive 10 free Live Arcade games. You just need to fill out this short form here.

Here's the list of games you both get:

Every Extend Extra Extreme (E4)
Sonic the Hedgehog
Street Fighter II - Hyper Fighting
Bomberman Live
Marble Blast Ultra
Spyglass Board Games
Small Arms
3D Ultra MiniGolf Adventures
Assault Heroes
Zuma Deluxe

Actually it's for most Europeans:

"1. This promotion is open to residents of the following countries; United Kingdom,
Ireland, France, Italy, Netherlands, Germany, Austria, Spain, Belgium, Switzerland,
Portugal, Greece, Sweden, Denmark, Finland and Norway, except employees of
Microsoft Corporation (“Microsoft”) and its affi liates, contractors, agents and their
families, and anyone else directly or indirectly connected with this promotion. Microsoft
reserves the right to verify the eligibility of entrants and check their identity."

Good idea, Nintendo take note.