iOS, Windows and Mac: If you want to remotely search your Windows desktop from your iPhone, iPad or iPod touch, X1 Mobile Search can do that almost instantly.
X1's desktop app has been around for awhile, so if you've used it (or Spotlight on a Mac) you're probably familiar with how this works. You type in what you're looking for on your iDevice and X1 suggests results as you do. It'll even search inside ZIP files. You can view documents and emails directly on your device and even download them for offline viewing. Documents can also be shared with other applications or via email so they're not restricted to the X1 app. Setting it up is pretty simple, too, as you just install a little bit of software on your desktop computer and enter the code it provides on your iDevice. Once the code has been entered successfully you'll be able to search securely.
Overall X1 works well and it is very quick, although it would be nice if there were more supported document types like images and audio files. Also, there's no posted version of the server software for Mac OS X at the moment, but it does exist and you can download it here. Nonetheless, if you want remote search on your iDevice, X1 is a nice, free solution.
X1 Mobile Search (Free) [iTunes App Store]