For a while now I have been using the Sumatra PDF viewer on windows as opposed to Acrobat Reader (which is pretty much the standard). The main reason is this: when I am working with Latex or Tex and generating pdf documents Acroread is very annoying because it holds a lock on the PDF file. This means that part way during compilation pdflatex complains that is cannot open the PDF file for output. I then have to close Acrobat Reader, rerun pdflatex, and then open up the file and go to the particular page to see the changes. That entire hassle is eliminated with Sumatra PDF.

Sumatra PDF does not hold a lock on the file. Which means pdflatex runs to completion just fine. Further Sumatra detects that the PDF file has changed on disk and refreshes itself! When it does this refresh as far as possible it stays on the same page (it does not do an effective restart) and hence I can see the little edit I made immediately. Sumatra PDF is a bit slower that Acrobat Reader, has less features and has crashed on occasion. Despite that, it says me a large amount of time when working with Latex. Highly recommended for these purposes.

Sumatra PDF

http://blog.kowalczyk.info/software/sumatrapdf/

MikTex

http://miktex.org/