I learned a bit about ocelloids on the most recent This Week in Microbiology - they are essentially eyes, complete with lenses and retinae, yet they're part of single-celled protists. In case it's not strange enough that a single-celled organism has an eye, it looks like ocelloids may have evolved from chloroplasts. This suggests that the most primitive* forms of light perception were developed by cyanobacteria. Thanks, bacteria.
* Calling a perfectly functional evolutionary development "primitive" may be unnecessarily pejorative here. Development of eye precursors is nothing short of amazing.