For my first project with the SparkCore I am going to rehash one of my old temperature sensor projects and have it post its temperature data over Wifi to a service like Xively. The cool thing about this is that you basically set it up once and it is a real IOT device that can send useful data to the cloud for as long as it is plugged in. You can even easily remove the device and bring it somewhere else and simply reconfigure to the new wifi settings from your phone to get it posting again.
I have another version of similar temperature monitoring projects here:
(xively used to be pachube, then cosm but its the same service)
The new idea with the sparkcore will be so much better because of its small size and lack of anything other than a power supply, and I am going to try and build the entire thing into a small “wall wart” plug. I haven’t decided yet if I should use the SHT21 or the DS18B20 (I have used both), but I will post details and pics on my blog as work through the idea. Feel free to give me feedback or suggestions on the idea if you want, I am VERY excited to get started with the SparkCore!