If you're in Column View in the Finder, select a PDF and you'll see a preview of the file in the rightmost column. There are two next and previous arrows to switch pages, but you can also scroll using two fingers (or a scroll wheel on a mouse) to move through the document.
[kirkmc adds: This works with PDFs, but it doesn't work with Word documents, which seem to have recently inherited the next and previous buttons in Column View previews.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120821155314289