ThingSpeak - Open source data platform for the Internet of Things. ThingSpeak Features
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
The IoT Guru - the IoT cloud backend company
AskSensors - The easiest IoT platform
dweet.io - Ridiculously simple data sharing for the Internet of Things.
Xively - Xively offers an Internet of Things product relationship management solution for enterprises.