I found this I Spy sheet on Scribd which can be downloaded for free. Some of the images are a little odd, but whatever. I added a document on Google Docs (here) which has a list of the items in the sheet (notations about which ones look a little odd and might be hard to identify) and has a few searches listed out to better make it into an activity. There's a screen to check the 4 quadrants, a listing of animals, and a few common letters listed out.
Happy visual hunting!