Our site -- https://www.PikaPay.com, does Bitcoins via Twitter.

If you're interested please take a look. Still a lot of work to be done, but we welcome any requests, suggestions and criticisms you might have.

As announced at the San Jose Bitcoin Conference in May, we've built an enterprise API that's open to everyone. (See https://Github.com/PikaPay ) An integration with Coinbase is already in the works.