Though Google may be the one of the most common search engines, there are others which are available as I have already mentioned.
Two other search engines worth trying out are Carrot2 and Behold. I have already mentioned Quintura for Kids and would like to point out how Quintura (based on a visual search engine technology) also offers an interesting alternative to Google.
Carrot2 is a cluster search engine and provides options such as images, wikis, and web sites. When reading the results of your search, you can immediately see which sites would be useful for your search. Here, for instance, after typing "environment" into the search box, you can easily read the menu on the right and decide whether you want to continue searching on one of the topics it provides, or keep scrolling down and see what pages it shows you.
Behold is a visual search engine which you can use to find images which are free to use and under Creative Commons. It also provides you with the link to ImageStamper, which is a free tool that allows to keep track of images under the Creative Commons.
Which of these search engines have you found to be the most useful?