Personally I don't think that Spectrum is a valid replacement.
I can't live without Freakscope, and that's because it's in a floating window.
Also because of the fact it's in a floating window I can use more than one instance of it at the same time on different tracks for comparison purposes.
I can't do this with Spectrum.
Another alternative is Voxengo SPAN:
http://www.voxengo.com/product/span/
The main thing that still for my mind makes Freakoscope better is it's refresh rate is SUPER SUPER fast and it's metering super precise with a very high FFT resolution.
SPAN is much slower and allows smaller FFT window sizes for the same refresh speed. It's main advantage is the ability to meter multiple sources simultaneously and be able to display the multiple FFT's on the top of each other. Excellent for comparison purposes.
You could also try a number of plug-ins by Blue Cat Audio:
http://www.bluecataudio.com/Main/Home/, but personally I didn't like their stuff much at all. I found their interfaces clunky, not particularly straight forward to use, and they had slow refresh rates.
