Books have been written on how to use Google more effectively. It’s becoming something of a science by it self. Joost De Valk have posted on his blog a cheat sheet PDF file on the url parameters and their meanings (Thanks Search Engine Journal for the reference).
Also, I came across this recently. Search Google Images for Richard Stallman on Google Images. Now search again by clicking here. What happened? Notice something different? Nothing but face images. How? Thanks first to Luis von Ahn and his Google Image Labeler game, now you can add a small parameter to Google Image results and get face images only. To do so, after you perform the search, simply add &imgtype=face to the end of the resulting url. Enjoy!