First of all, if you have a Starbucks card but have not registered it online, do so by TOMORROW, March 14, and they’ll give you a $5 credit. From what I understand, any Starbucks gift card can be registered and then it becomes “your” Starbucks card, which you keep forever and use to keep track of how many coffees you’ve purchased so they can give you rewards.
Second, there’s this coupon out there fore a free caramel or hazelnut macchiato, valid through the end of March. The blog post I linked to there links to a printable version, but be warned that it is not from the Starbucks site. From this Money Saving Mom post and the comments on it, it seems that some Starbucks stores are handing out paper coupons for the freebie, while other stores just give you a free one if you ask or mention “discount code 350.” If you don’t want to print the coupon, you could always just ask at your local Starbucks. Best of luck!