Update: Pachube is now called Xively.
Pachube is a service that enables you to send in sensor data from Internet-attached devices and then monitor and refine that data over time.
Right now it’s mostly for experimental use, but there are serious applications as well.
As is the norm nowadays, Pachube can be accessed via an Internet API both for inputting data and to monitor the data.
There are numerous applications, including mobile such, for using the recorded data: Pachube – Internet of Things Application Repository, and of course you can make your own as well.