LilyPad and ATtiny 

The LilyPad family of Arduino compatible platforms are great for designing wearable tech whether you're prototyping or gearing up for CosPlay. They are built around a tiny but still powerful microcontroller, the ATtiny85. While the amount of memory that is available to hold a program is small, only 8K, it can serve as a challenging design limitation and also keep you from going crazy with too many features on your wearable dinosaur costume.

SparkFun has a great tutorial on how to get your Arduino sketch onto the LilyTiny. We are using it as our guide for this tutorial.