Here you can find all the small projects realised with microcontrollers.
And for all the fanboys of PICs or AVRs: I still use mainly Arduino, but sometimes the PICs are sneaking their way into projects too. I don’t want anyone brag about “mimimi, my system is better because I used <insert µC here>”. Everybody can choose the µC he wants. Both systems are similar, but as it seems the PICs are getting more expensive currently.