We use flexiscale. It does have an api, its just web-based (https://api.flexiscale.com/current/doc/). We have worked closely with their engineers to create a simple desktop app for managing/viewing server status (http://cogniscale.cognifide.com/). This work is on-going.

However, EC2 is a great platform. Flexiscale is an alternative but EC2 is much further down the line. I'm watching this space.