Warning: Google Games mentioned here may be highly addictive.
Toogle Search - Bill Gates - When you make a search on Toogle, it fetches the first images from Google images search and converts the picture into a colored ascii file made of only the search terms.
Google Mirror - elgoog - This site is like a mirror reflection of Google. All the text is displayed in the reverse order and inclined to the right of the page just like Arabic language. Remember that the queries are also to written in the backward direction [live example]
Gwigle - What Am I Googling? - A very addictive game where you are shown the Google search results page and you then have to reverse guess the search query. The game has various levels and can keep you busy for a long time. The accompanying tips will help you become a better googler. [Thanks, Ionut]
Guess The Google - At the start of this Google game, a grid of 20 image thumbnails would appear each of would match one search keyword. You get 20 seconds to guess the search keyword but you can make as many number of guess as you want during that time.
Googlewhack - A Googlewhack is a Google search query consisting of two words - both in the dictionary, and without quotation marks - that returns a single result. The search will list 'Results 1-1 of 1'. Googlewhacking is the pastime activity of finding such a result. A person attempting to find Googlewhacks is known as a Googlewhacker. [Whack Stack]
World War on Google Maps - Online players (2-25) randomly receive a set of countries with troop hitpoints based on real world population data. To play: attack neutral and enemy countries in an effort to try to take over the world. You have a 20% chance of receiving more troops when you overtake an enemy country. [via Slashdot]
Google Maps Flight Simulator - Nothing so advanced as the Microsoft Flight simulator, but this Googel computer game lets you fly a small farmer plane over any landscape created from a compilation of Google Maps images. You can use the keyboard arrow keys to change the flying directions, bank and dive. Space lets you fire while A/Z are for varying the flying speed.
Guess the Place - You are shown a picture and need to find out which country, state or city is being shown by looking at parts of Google Maps, or Flickr images of the place. [Philipp Lenssen]