What tools are available for (easily) managing drawings similar to the software architectures published by Amazon, such as this one. I'm looking for something like OmniGraffle or Visio, but suitable for Isometric.
Google search for "Diagram software with 3D" and the first thing that comes up is edrawsoft which does exactly what you want.
Adobe Illustrator, CorelDraw, Autocad, Xara, Freehand, Inkscape.
Essentially anything which can create vector output should be able to create isometric objects with relative ease.
And of course almost any 3D application would work.
Aahh... I had a simmilar question about a year ago, check it out here:
One good thing would be: CAD Tools for Adobe Illustrator
But there are more plugins(cheaper) and other ways to get around isometric graphics...check out the question I mentioned above.. and my chosen answer is here: https://graphicdesign.stackexchange.com/a/4944/1392
This stuff seems easy at first..depending on the task, stuff with isometric graphics can get pretty complicated.