"PDF Presenter is a free PDF presentation software to display your PDF documents through an external projector."
This is handy if you want to show slides in PDF format. There are also whiteboard tools allowing you to annotate with a mouse or pen (if you're using interactive technology: IWB, IVP etc).
Download page > http://pdfpresenter.sourceforge.net/
Via Baiba Svenca, Shona Whyte