The ecosystem of new application and platform services in the cloud is the future of application development. It will drive rapid innovation and we'll see a wealth of mobile, web and desktop applications arrive that we couldn't dream about a few years ago, and these building blocks are the enablers of that. These services will be delivered not only by new startups but also by enterprises looking to capitalize on their IP.
As examples of such services I always use Twillio (voice &sms) and Simplegeo (location), but it is time to start building out my knowledge of all the different services that are in the ecosystem. If you run such a service or know of one that I should be checking out, please leave the info in the comments below. I'll be using that information in presentations and some future writings on this topic.