http://www.google.com/cse/ provides a facility to offer custom search engine to your website, blog. It also allows you to offer to your readers custom Google search engines that search specified sites and provide results.
For example the following the two custom search engines one for searching Knol and the other for searching YouTube
Google Knol Search Facility
YouTube Search Facility
http://code.google.com/apis/gadgets/docs/basic.html provides information on Gadgets.
Hosting the gadgets requires an editor and Google provided http://code.google.com/apis/gadgets/docs/tools.html#GGE for hosting gadgets