Melda Analyzer is one of the best free availabel. IMO
Usability is not the best. Its hard to get used to the UI but u can tweak more or less as mutch as in voxengoSPAN.
And it works fucking fluid, for me. And it has no anoying demo feature like SPANPlus (turning down volume).
[Edit: I used Voxengo SPANPuls which is the paied version of the plugin. Get VoxengoSPAN and u have no trouble]
I have digged abit throu the rest of the free bundle and think the Noise generator can be usefull. Maybe Ring modulator. And the StereoAnalyzer (Vectroscope/Goniometer) is nice too.
Meldas Waveshaper is imo not as usabel as fuityWaveshaper.
If u have no good Spectrum analyzer and want one for free i would get this one.
Biggest downside IMO is that u can't look at frequenzes higher than 20kHz.http://www.meldaproduction.com/plugins/product.php?id=MFreeEffectsBundle
Better then voxengoSpan or BlueCat stuff.http://www.voxengo.com/product/span/http://www.bluecataudio.com/Products/Product_FreqAnalyst/
Other free analyzer i looked at. http://mdsp.smartelectronix.com/freakoscope/http://sevenphases.wordpress.com/spectrum-analyzer/
While writing this i found this site.http://blog.wavosaur.com/best-free-vst-plugins-for-analyzing-audio/
I will check out this. -> Flux Stereo Tool
Still Searching for a nice (free) Oscilloscope Dont like the "wave candy" stuff of fl.
S(m)exoscome isn't nice enough IMOhttp://bram.smartelectronix.com/plugins.php?id=4