Sennheiser Frequency Finder - iPhone app and website
 

I was in the market for a wireless lavalier system. Sennheiser was one of the brands I was looking at. While visiting their website for product information, I came across a nice tool. They have developed an iPhone application that checks your GPS coordinates and lets you know which frequencies are free to use at your locale (i.e. not used by government, television etcetera). They have also developed a new website with the same functionality. It is called Sennheiser Frequency Finder, you can find it at:
Sennheiser Frequency Finder (BETA)

At this moment, it is only available in Europe for use in The Netherlands, Belgium and Luxembourg but it states that more countries are following soon. I think this is a great idea. I don't see why Sennheiser can't develop something similar for countries outside of Europe. They most likely will.

At the end, I bought an Audio-Technica system but the Frequency Finder is still a great tool to use!