Freeware - SIR Audio Tools Spectrum Analyzer VST Plug-in

http://www.siraudiotools.com/Spectrum-Analyzer.php

SpectrumAnalyzer is a state-of-the-art spectrum analyzer plugin, which offers a lot of opportunities to display the spectral content of your audio material and helps you create a better mix this way. SpectrumAnalyzer comes in two editions, a free and a full version.