you can build a nice & very simple array where each pixel is a photoresistor in series with a diode. Then you wire & multiplex the array just like you would an array of LEDs. Using just the Arduino you could do a 6x6 array (since you've got 6 analog ins). If you added multiplexers you could really scale things up...
Have you checked out Jeff Han's work?: Jeff Han, NYU Courant Institute of Mathematical Sciences
& of course johnny lee's projects are awesome & relevant: Johnny Lee's website has moved
good luck!