I only know Windows based tools, but I will say that I use MetaGeek's InSSIDer and Ekahau's Heatmapper. There are also other free tools out there for plan/designing offices and home. These are provided by Wi-Fi infrastrucutre companies Aerohive and Meraki. Also, I know that Xirrus has a Wi-Fi inspector that is a program and gadget for Windows Vista/7.


Here is a list of links:
Metageek InSSIDer: http://www.metageek.net/support/downloads/
Ekahau Heatmapper: http://www.ekahau.com/products/heatmapper/overview.html.
XIrrus Wi-Fi Inspector: http://www.xirrus.com/Products/Wi-Fi-Inspector.
Aerohive Wi-Fi Planner: http://www.aerohive.com/planner
Meraki Wi-Fi Planer: http://www.meraki.com/products/wireless/wifi-mapper

There are tools out there for the OSX, but I don't use them so I don't want to recommend what ones are out there.