BlueCat FreqAnalyst and BlueCat's other freebie plugins updated - 01/12/14 05:49 AM
FreqAnalyst is a really nice spectrum analyzer plugin that allows overlay with an opacity/transparency adjustment (so you can compare content in multiple tracks.
http://www.bluecataudio.com/Products/Bundle_FreewarePack/
http://www.bluecataudio.com/Products/Bundle_FreewarePack/