Skim

skim-mainWindow.jpg Skim is an application that is for pdf viewing, but not just any pdf viewing. It allows you to take notes on the pdf, take snapshots, highlight, and have all sorts of other types of navigational goodness.
It reminds me of having microfiche back in the day at a library, and taking notes along side while taking a look at it, then making copies of the microfiche. Crazy how we’re not entertaining new ways of note taking and pdf reading. You literally can just skim pdfs while interacting with Spotlight, bookmarks, and it even has PDFSync and LateX capabilities.
Very hmm… educationally driven. Free for MacOSX.