Here is an open source hardware kit with everything you need for prototyping. Tinylab has a compact design but comes with an Arduino, modules, circuits, and everything you need to get started. You get sensors, Bluetooth support, buzzer, DC motor driver, a LCD display, LEDs, buttons, and more.
Tinylab is easy to use. Just remove the cap, connect it to your computer, and upload your sketch. You can use Eclipse, Scratch, Codebender, and other environments to get started. More information is available on Indiegogo.