They're called Real Time Spectrum Analyzers...

Here's a few;

http://www.fullcompass.com/product/284624.html
This is the model I own. It's decent, accurate and very portable. It's drawbacks are that it does not come with a rack mount kit and the ranges can actually be too narrow for mixed volume content.

Acid 8Packs
Heard some good things about the True... just be sure your A/D's a good high quality unit.

and there's the perennial favorite of
http://www.purebits.com/

Sticking with hardware based...
http://www2.rohde-schwarz.com/en/products/test_and_measurement/product_categories/spectrum_analysis/FMU36.html

http://www.home.agilent.com/agilent/product.jspx?cc=US&lc=eng&nid=-536902959.536881891

Assuming that's a bit of overkill...
http://www.phonic.com/en/other/testers/paa3.html

Bonus.
Owe you one.

Btw, your SA3051 does have a rack mount kit optional.
http://www.fullcompass.com/search.php?search_simple=true&txtAll=rm-10
Even.

ALSO

Acid 8Packs

Cheers for all the links guys.
That Phonic Paa3 looks tasty.
I would love to splash out for one of those big beasts but it really just seems like a good quality calibrated mic, preamp and D/A with handy switches.
Maybe I can mix and match, get a calibrated mic and use my laptop to do the analysing. I will be researching further.
Thanks once again.

Greener wrote: ... Matlab is a devil...

I'm considering using Matlab for this on a limited basis , so I'd be interested in what you are doing.

I'm going to be teaching a course in partial differential equations next academic year, and I'm thinking about what software to use for visualization. I also do a bit of comparison of calculations to real data (using room acoustics as an example). It would be nice to do a bit of real time analysis with standard mathematical software. I'll probably use Mathematica, but a lot of our students use Matlab. I may not go beyond identifying room modes, but I'd like to know what you have done with Matlab.

I wouldn't be using Matlab in realtime. You probably could but my head would melt before I got output.

There's a cheap version of Matlab. Can't remember the exact name but I'm sure it's only one letter off.
Apparently it has 90% of the functionality for either dirt cheap or free.