I have created some Greasemonkey User Scripts before, but this is the first one that could be used by others. All other were only fit for personal use. This script will add links to other search engines when searching for something on google. For example, when you search for anything on google, the result page will show the following line...
Try your search on Yahoo, Ask Jeeves, AllTheWeb, Teoma, MSN, Lycos, Technorati, Feedster, Bloglines, Altavista
I got the idea from a Firefox extension which did the same thing. I thought that making a extension for such a simple task is bit of an overkill - a simple user script will suffice for this purpose.
For installing these scripts, you must have Firefox browser and must install Greasemonkey extension for firefox. Then right click the below link and choose 'Install User Script' Option from the context menu.
Install Multiple Engine Searcher.