http://www.web-ee.com/Schematics/AudioAnalyzer/AudioAnalyzer.htm
using CATV tuners
http://www.nitehawk.com/rasmit/sa50.html
This 3 channel 15 LED spectrum analyzer can be used as an addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range
http://www.aaroncake.net/circuits/3chspec.htm
a device which will display the strength of all FM Radio stations simultaneously.
http://www.ee.washington.edu/circuit_archive/circuits/ee498/final/index.htm
for the home experimenter
http://www.arrl.org/qex/Henkel.pdf
capable of useful measure-ments in the 50 kHz to 70 MHz region. The design can be extended easily into the VHF and UHF region
http://www.arrl.org/tis/info/pdf/9808035.pdf
for spectrum analyser
http://www.mrs.bt.co.uk/dubus/9202-2.pdf
freeware FFT program for Windows
http://www.relisoft.com/freq.zip