Commercial software

Symantec Visual Cafe for Java
A commercial Java development environment, which I bought one copy of. You can try it out, but please be careful as we do not have a site license.
Adobe Acrobat Reader
Yah, it sucks, but ya gotta have it.
Aladdin Ghostscript
OK, not commercial, but it goes with Acrobat. You need all of these:
Macromedia Freehand
Freehand (back in the days when it was called Aldus Freehand) used to be the best diagramming program for the Mac. Version 7 costs $125 at Scholar's Workstation, but I wouldn't buy it because version 8 has been announced. You can download a crippled demo (no file saving, exporting, or help (!)) from their site.
Visual Thought
A tool specifically for drawing box and arrow diagrams! Runs on Windows and Solaris.
Adobe Illustrator
The competition to Freehand, I guess. You can download a crippled demo version.
Mayura Draw
Hey, this one appears to be free! You can apparently use it to edit Postscript files (in conjunction with Ghostscript), and generate vector graphics in PDF.
Visio Professional
Visio, I have been told, is the best drawing package for Windows... Unfortunately you can't download a demo program and they don't even put prices anywhere on their page, but you can request a a demo CD:
Adobe PageMill
I am interested in seeing if the visual site builders are any good. Adobe have demo versions of their 2.0 product and their 3.0 beta product. When I installed the 3.0 demo on my home machine, it complained about the file "urlmon.dll" missing. So below is also a copy of one I pulled from the version 2.0 demo.
Microsoft FrontPage
MS FrontPage appears to have pretty good navigation support... It's also easier to get than PageMill..