I’ve got a Starbucks card for when I’m out in Dallas, and I like it! It’s basically a pre-paid card which you top up in Starbucks stores and then use like a debit card when you’re paying for your Mocha or Frappuccino.
Rumour has it that they will be launching them in the UK very soon. There’s no real benefit to having one (although they sometimes run special offers etc.) but they tend to look quite cool, and they’re handy for gifts as well. Just in time for Christmas!