Which AI startups seem to be succeeding?

MetaMind and Sentient Technologies come to mind for me, in terms of independent AI startups. MetaMind provides APIs for particular AI jobs and designs the backend for them. Sentient Technologies appears to be a more research-y company. I think some of the best teams overall in AI probably exist in the larger companies, like Facebook AI Lab or Google DeepMind or Google Brain. Also keep in mind that AI is still a very nascent field, with high knowledge barriers of entry and limited applications (with respect to similar fields like machine learning).