MacGizmo

MacGizmo is an application that allows you to see the content and other useful information of any selected items in the Finder and of other participating software programs.

It is very easy to use: select an item and see the content.
MacGizmo currently fully supports most of the common kinds of items that populate a disk, like: images, sounds, music, video, text, pdfs, Web files, fonts, folders, applications and many more.
MacGizmo does not just provide a preview, it also allows you to navigate as a Web browser, have full access to pdf and text files, read help and the recent items opened by an application simply by selecting it, hear music, see videos and, where applicable, print and search content.