Paweł Spychalski build a photoresistor based daylight meter sensor connected via I2C bus using ATtiny85:
I love AVR ATtinyx5 series microcontrollers. They are cheap, easy to use, they can be programmed just like Arduinos and comparing to their size they offer great features. For example, they can be used as remote analog to digital converters connected to master device using I2C bus.
ATtiny85 Light Sensor – I2C slave device – [Link]