A classic project, re-told on the MSP430 Launchpad's MSP430G2221.
Glass jars of LED fireflies which synchronize over time. A piezo transducer in the lid detects tapping and randomizes the pattern.
MSP430G2221, 7 LEDs, 2 resistors and a piezo transducer. Cheap and simple.
Eagle CAD design files: http://wp.hodgepig.org/wp-uploads/2010/ ... agletar.gz
Source code: http://wp.hodgepig.org/wp-uploads/2010/12/fireflies.c (mspgcc)