WinQuickLook

The OS X Quick Look feature is often missed by users who switch to Windows, and understandably so; it is very handy, as it provides you with near-instant previews for a broad range of file types.
WinQuickLook can provide you with a solution, offering similar functionality to that enjoyed by Mac users. It supports several popular formats, but it still needs a few more improvements.

Preview content instantly without opening files

Once you have installed this application, you need only select a file and press the Space key. A quick preview of its contents will be displayed on your desktop, provided the format is supported.
Just like on a Mac, the preview will be updated automatically if you use the arrow keys to select another file in the same folder.
Of course, you also have the option of opening the file with the default application by clicking the “Open with” button in the top-left corner of the window. Sadly, though, the name of the application is not displayed.

Lacks support for some popular formats and needs a few small improvements

The program supports a decent set of file formats, but a complete list is not provided. We were able to open images, videos, audio files, TXT files and Microsoft Office documents, but PDF and archive files do not seem to be supported.
If you preview a video or audio file, it can be played directly in the WinQuickLook window. Again, it is not clear which formats are supported, but we had no issues accessing most media files during our tests.
Text wrap is not used, so reading some documents could prove to be difficult. It is also worth noting that Microsoft Word files are not split into pages, and we found that the preview window often took up a bit too much screen space.

Not quite Quick Look for Windows, but it comes close

In the end, this application still needs some more work before it can be considered a true Windows version of the popular Mac OS Quick Look feature. Support for more formats would be the most important addition, followed by a few tweaks to the preview window.