Affordable space planning software for group living

What affordable or free software packages are out there to help me visualize a new living space? I would like to be able to hit the ground running and start planning right away. I have an older copy of MS Visio which I love, but doing that much drawing there would take way too much time.

I’m moving into a large home and will be living with three additional people (five total plus pets), and we need to establish which rooms are to be used for what fairly quickly as there are some strong opinions about certain things. Since I will be facilitating most of this process and I rely on visual aids for stuff like this, I really need to get this onto a physical or ditgital canvas ASAP. I’m also going to be responsible for setting up our new LAN and the other folks do not understand network topography at all, so this will also require a visual aid.

I like Floorplanner. Great suggestion.

Also found/rediscovered Google Sketchup. I may also consider The Sims 3 in the future.