In a close race I would have to say Copernic Desktop Search. It's a very competent and balanced product and one of the few freebies that supports network shares. My only beef is the presentation of email search results is not as effective as other search engines such as X1, a product that is unfortunately no longer available in a free version (although it is integrated into free email client Eudora's find function)

Another option is Google desktop search. It not only will search your hard drive files but also your web history. It offers an Outlook toolbar, integrated Gmail search and a novel desktop sidebar that allows personalized search, news, weather, photos and more. The Sidebar also includes a quite effective application launcher. Some folks love the Sidebar but others, me included, find it intrusive. My main problem with Google Desktop search is again the presentation of email seach results which is even poorer then Copernic. This is not an academic point. For many users searching email is the number one application for desktop search programs so you need a product that performs well in this area.

Locate32 is a little known but highly impressive desktop search program. It works like updatedb and locate commands in Unix based systems. In other words, it uses databases to store information about directory structures and uses these databases in searches. The use of these databases provides very fast searching speed. The software includes a dialog based application as well as console programs which can be used to both update and access databases. Supported operation systems are Windows 98/ME/NT4/2000/XP/Vista. Locate32 does NOT have to be running at all times like both Copernic and Google desktop. In my tests, it wasn't quite as fast as either of the above, but it is still quite fast. Plus, I really like not having to have it run all the time. Just remember to update the databases fairly regularly. Please note that finding words within files is somewhat difficult to find. At first, I didn't believe that it included this feature, but it is included. You just have to look to find the feature. Available in many languages.

Everything (http://www.voidtools.com/) indexes your entire hard disk and then you can search for a file by typing in part or all of the filename and it will display results as you type. Then just double click to run the file or right-click for the menu to open the path. The beauty of Everything is that it can be completely portable!

Cons: It does not have a right click preview of common file types (txt, doc, pdf, etc.). It works only on NTFS drives. And, Everything does not search file contents, only file and folder names.