This is cut and pasted from another blog, so I'm not taking credit for it. (But I took out some of the things that I didn't think sounded like all that much fun.)
10 Tips For Google Image Search
6. Find random personal pictures, using standard file names from digital cameras.
8. Install a Greasemonkey script so you can view the original version of the image directly by clicking on the thumbnail.
9. Find the color of a word. "Word Color is a windows program that uses Google Image Search to determine the color of a word or string of words. It goes out there, retrieves the top 9 images and loops through all pixels, calculating the average hue, which is later converted to a color."
10. If you want to grab search results, GoogleGrab is a tool that downloads images from Google Image Search. It even supports batch search.