Discover Card is running a pretty solid cashback promo right now that expries on Jan 10th 2012. Right now, they will give you $100 cash back (for new card holders) if you charge $500 within the first three months. Even if you only charge $1, you will still get a $50 bonus. Not bad.
The catch is you need a referral from an existing customer, but I found a few here: www.easymoneyhacks.com.