Zetadocs PDF
Adobe's PDF (Portable Document Format) is pretty much ubiquitous these days, its main advantage being that PDFs are hard for users to edit, which provides a measure of control over distributed information. PDF also copes well with graphics-rich material, locking it into a layout that reproduces accurately on a wide range of platforms. Finally, Adobe's PDF reader is free, so there's no cost barrier to access (you can download Adobe Reader <a href="http://downloads.zdnet.co.uk/0,39025607,1,00.htm?query=Adobe+Reader">here</a>).