Google Simple Search Gadget
Google Simple Search is a free and safe Windows gadget, just a small search bar on your desktop to let you perform easily global internet searches.
If you reduce the opacity of the search bar to 20% it will disappear almost completely, coming to full view only when you click on it to write your search terms. There are two possible sizes of the search bar. The default is small, but there is also a large version, in case you often search for a lot of terms in a row.
Check also SearchALL free Windows Gadget, if you like to search more than Google.