I have been playing with Floorplanner.com
It's a well done website that allows you to draw your own plan in 2D then view it in 3D.
The learning curve is not to bad, even if you have never used a CAD program before.
It had even improved since the first time I tried it to draw my basement floor plan.
I managed to draw a computer lab to show concepts to my colleagues.
Create an account to try it free.
If you really like it you can pay for "Plus accounts" and get more space for more plans.
Check out a diagram I did here, be sure to click 3D. I used the Green telephone booth's to represent server racks. As with many 3D flash websites, it really helps if you have a fast CPU and lots of Ram.
