Well... If you're looking for Mac OS X native software, it seems you're out of luck. I need this kind of software myself and the good ones cost a lot of money and only run on Windows.
I would pay for a wireless LAN planning software, be it for Mac or Windows, because I do professional site-surveys. For now, I can assure my clients that their network does or will work, based on a ping test, along with RSSI (signal) and SNR (signal to noise ratio) readings. It would be more convincing if I could show them a graphic representation of that, which is what you need -- the so called "heatmap".
If you're savvy enough, this guy (
http://slowchop.com/2008/08/17/wireless-heatmap/) managed to write a software (in Python, which should work on a Mac) that does just what you need. I haven't tested it, though, because time is scarce here.
It needs airodump-ng, which is available for Mac as part of aircrack-ng (
http://www.aircrack-ng.org/). Download the source, apply the patch and install it. Then, follow the instructions on the guy's website.
This also looks like a great opportunity for a programmer to create a Mac OS X native version, maybe using Py-ObjC or porting it all to Cocoa/Objective-C. I wish I could do it.
Message was edited by: fdonadio (corrected english mistakes and provided some missing information)