UPDATE: They're going to release keys sometime during PAX Prime 2012, that's about now-ish.
Alienware Arena is giving away some League of Legends promo keys. The key unlocks Samurai Master Yi; if you do not own Master Yi and redeem this key, you'll get both the champion Master Yi and the Samurai Master Yi skin.
Patience is a virtue since their website is getting hammered. On the other hand, the keys are limited and Alienware Arena is giving away these keys in batches--first batch of keys have all been claimed.
Note: These keys are region locked and requires an account with Alienware Arena to claim--I recommend registering first in case the site gets hammered again.