[NEW: GhostScript has now a much improved PDF conversion, which has been used to include PDF versions of most files. Use right-click or shift-click as described below if you want to download without opening Acrobat Reader first.]
The decision on file formats for reports, etc., is a bit tricky. PDF is convenient, in that many have Adobe's Acrobat Reader already installed, and if not, it is easy to download and install. Some files here are in that format. Viewing and printing from Acrobat is straightforward.
I write mostly in LaTeX, now usually producing PostScript (PS) output with dvips. A PS-compatible printer can be used for hardcopy. Or use the GhostScript freeware emulator for output on almost any printer. For Windows I recommend Gsview (also free), which acts as a convenient front-end to GhostScript, and allows good quality viewing on screen. (Hint: unless your computer is very slow, increase the defaults for Text Alpha and Graphics Alpha in the Media.../Display Settings... menu.) There are similar viewers for Unix, Mac, etc. Gsview (and GhostScript) also handle most PDF files, and sometimes may be more convenient than Acrobat (for printing double-sided, for example, and printing quality can be better.) Some files here are in PS. Printing quality is good, but PS files can be quite large.
Gsview/GhostScript can convert PS to PDF, but currently with limitations. Specifically, they do not handle well fonts other than the standard resident PS fonts TimesRoman and Helvetica. It is possible to use PS fonts in LaTeX, which is what I have done for the PDF files here. Unfortunately, compared to the traditional TeX/LaTeX Computer Modern fonts these are ugly, and maths is done with bitmaps, coming out a bit rough. It would be better to use Adobe Distiller for PS to PDF, but it costs money :-)
A way around the large PS files is to compress them into zip files. I decided instead to use gzip, a public domain standard readily available also in Unix and other platforms. Conveniently, Gsview can open gzip compressed PS files directly, without having to decompress them first. These are the gzipped PostScript files. If you need to decompress them, for example for output to a PS printer, in Windows it can be done with the excellent WinZip shareware program, or on most systems with public domain versions of gzip/gunzip.
Important note: Under some conditions the browser insists in opening these files as text instead of offering to store them on disk. I am told that it is a web server and/or browser configuration problem, and that a solution is to shift+click on the link, instead of just click. With some browsers you can also right-click, and chose saving to file from the context menu.
Other files here are grouped and compressed as zip files (or archives.) These can be opened with the already mentioned WinZip, or with various other programs such as unzip, pkunzip, etc.