http://www.metageek.net/products/inssider/
There are many scanning utilities out there, however this one happens to have three things I really like
- Shows you a frequency overlap chart, which is rather interesting if you are trying to use 40 Mhz 24. Ghz band as you end up overlapping a lot
- It can graph over time, which when you are tweaking settings and antenna possition really lets you see if things are stable and improving
- It also clearly shows you 5Ghz networks (this only matters if you have 5Ghz equipment but it is interesting.)