If you like playing around with 3D room planner software, then take a look at ExhibitCore. It's an online web-based system which seems to be designed for those who work in the industry of designing exhibition stands. However, it can also be used to design all sorts of other room layouts.
To use the system, go to this page on the ExhibitCore site and create a free account (you'll need to supply an email address). You can then log in and start working on a 2D image from scratch, or load one of the many built-in samples. You can see the 2D design screen in the first screenshot below (To save space, I've chopped off the window of items such as tables, chairs etc that you can drag into place).
When you're happy with your design,simply press the 3D button and your plan is rendered into a three dimensional image, as shown in the second capture below. You can then fly around the image with the airborne camera, and there's even a walk-through option too.
It's great fun, very professionally put together, and a basic account on the system is completely free.
Editor's Note: Following advice from the website owner, the link to the website in the article has been updated and now takes you directly to the Exhibitcore Floor Planner launch button rather than the home page.You must launch the app before you can login.