Exploring how a component work, in detail, lays a great foundation for building a complete robot. RobotGeek supports this idea, with several Arduino-based kits designed to explore individual components. There’s a kit for linear actuators, one for touch sensors, and another for RFID.
Want a more complete package? Consider the RobotGeek Arduino Basic+ Experimenters Kit. In addition to an Arduino, it comes with a variety of components, including a tilt sensor, push button, slider, relay, buzzer, joystick and servo.
The Basic+ Kit costs $109.95 and can be purchased from Trossen Robotics.