Arduino is a great starting point for electronics, and with a motor shield it can also be a nice tidy platform for robotics and mechatronics. Here is a design for a full-featured motor shield that will be able to power many simple to medium-complexity projects. Build the kit, and learn how to use it with these detailed instructions.
The combination of connecting a Raspberry Pi to COSM makes creating a internet of things much easier than it has been in the passed. The Pi with it's easy access to ethernet and COSM's drop dead simple usability will graph all sensor data you send to it. This tutorial explains how to connect a analog temperature sensor to the Pi and use a small python script to upload that data for storage and graphing on COSM.