Register a Starbucks pre-pay card and not only will you get a free drink on your birthday, you'll earn 1 Starbucks star for each time you pay with it. Once you've accumulated enough stars, you'll be eligible for the following:

5 Stars:

• Add a syrup (most flavors) or swap in soymilk at no extra charge.
• Brewed or iced coffee or tea refills are free while you’re in the store.
• Buy a pound of beans and you'll get a free tall drink.

30 Stars:

• Free drink for every additional 15 stars accumulated.
• Special offers and coupons via email.

Update - As of October 16th, there will be the following changes to the Starbucks card reward program:

• Rewards are loaded onto the card instead of being mailed to you on a postcard.
• Rewards can be used to redeem food and drinks instead of just drinks.
• Gold level members are rewarded a free drink after every 12 stars instead of 15.
• There will be no more free soy, syrup, and tall beverage (with pound of bean purchase) rewards.