Quicklook is very useful, because it gives you a quick look of images, PDF, videos, music and more. So you already know it.
It is seemlessly integrated into the finder. You also can activate it by clicking a single or multiple icons on the desktop or in finder and just click space. It will open a transparent Quicklook.
But did you ever tried that with an archive or a folder? That’s not good. You just see a big icon and it does not make much sense. You can easily extend Quicklook with plugins, then it looks like this showing the content:
Folder contents within Quicklook
Just download the Extension for Archives and for Folders. Then unzip them and copy the containing qlgenerator files into ~/Library/Quicklook (the MacintoshHD, not user directory!). To let Finder know about that you can “relaunch” it by holding Option and left click the finder icon.