Scanning radio waves is fairly cool in the first place. Most people really don't have a clue what's going on and it's fascinating. There's an plethora of various services and devices in this area of spectrum.

http://www.ntia.doc.gov/page/2011/united-states-frequency-al...

Some uses I would consider besides general scanning and exploration would be: amateur radio (multiple bands), NOAA weather stations and satellites, various aviation services, device monitoring and prototype assistance, etc....

slow scan tv receiver for ARISS (Amateur Radio on the International Space Station). i implemented this as part of a class project using $20 tv tuners hacked into a crude sdr. http://inst.eecs.berkeley.edu/~ee123/fa12/project.html

Well, there's roughly a lifetime of perfectly legal technological entertainment if you bother to get licensed and operate under FCC part 97, for which this gadget would make an interesting toy/tool.

You could read more about this topic at http://www.arrl.org/

Your own GSM network for one. http://gnuradio.org/redmine/projects/gnuradio/wiki/Introduct...

Transmit and spoof things (i.e. pretend to be other devices)?