The Google Desktop
A beta version of the Google Desktop is available for download that enables you to search through all of your Outlook/Outlook Express, Word, Excel, PowerPoint, text, and AOL Instant Messenger files and data. It even searches through your Internet Explorer browser cache so you can view matching web pages when you're not online. As an added bonus, it indexes filenames, so a search for "dad" would find your "Mom and Dad.jpg" and "Dad's New Car.jpg" photos, even though you haven't tagged those files with any metadata.
The Google Desktop installs an icon in your system tray and indexes your data during idle time. To search, you simply double-click the tray icon and a browser window appears that looks very similar to the Google web site. The results page also looks just like a typical Google search. And, if you can't find what you're looking for in your own data, you can click on a "Search the Web" button to submit the same search for an online query.
It's a very fast search that seems to give results that are similar in quality to the online experience. Overall, I think they've done a fantastic job with this. I hope that our upcoming search technologies can equal or exceed what they've demonstrated here. For more information, read this O'Reilly Network article.