Have you ever lost a document that you were sure was on your system? I've been in a few situations where both Windows search and Google Desktop have failed to locate a lost document. Often, the problem is that the documents have been zipped-up or compressed. Step in EF-Find which is a small but powerful search program for Windows that can search for not only lost files but also text, HEX sequences and regular expressions inside compressed archives.
For example, if you've written a document about networks but just gave the document a generic name, you can search for 'networks' in EF Find, and even if it's in a compressed file, it will find it almost immediately. The range of files it can search is really impressive and extends to 7-Zip, ACE, RAR, ZIP and many other formats. Like with all good search engines, you can also filter searches to such things as those words in upper case or within specific folders. This simple program has already been translated into 23 languages which gives some measure of how useful it is.
The only downside is that it can't search within documents that aren't compressed but as long as you've got lots of zipped-up files, you might find EF Find proves really useful one day.