pegasixi:
Out of curiosity, can you/anyone recommend a good analog LDR with good resolution in a small package? I'm along the lines of using a cheapo laser, pass it through a filter, pass that through a pinhole (to decrease the size of the dot and increase accuracy), and have the LDR detect the tiny remaining LED dot.
If you are using a bright light source of with a known output primarily at or around a specific wavelength (like a laser or LED), you could use discreet photodiodes or phototransistors. They can come in very small packages and can be biased to specific threshold levels. Here's an example of a photodiode is made to detect red and near IR and a small and thin package. To give you an idea of cost, Digikey's price is $3.64 for volumes under 25.