My 1st experiment: there's a variable which increases with time. One led blinks when it increases, the other blinks when the variable is multiple of 3.
http://www.youtube.com/watch?v=uNxOBWpxz98

Here 3 leds oscilate just like in a three-phase system.
http://www.youtube.com/watch?v=kS-0d74mtTA

On this one I used an LDR to control the luminosity of an LED
http://www.youtube.com/watch?v=K2bKod58P-k

At last, I merged the last 2 circuits, so the leds blink and I can control the intensity:
http://www.youtube.com/watch?v=JNjJlN3vNIQ

Looks cool, I've been working with arduino's at work too, awesome system.

Got one at home too, just can't think of any cool things to do anymore, it's impersonating a binary clock now