Spectrum analyzers and oscilloscopes are fun.  Before too long you'll be looking for odd stuff everywhere to analyze.  Don't ask me how I might know this..  
 
John

wave on...
which are the good ones at a nice price?

Didn't The Ron bring a software based spectrum analyzer (running on an OLPC, no less!) to the Northern Cal get-together?
 
Perhaps Mica might know more?

Turn the volume all the way up on the guitar, plug into the tuner, pluck the harmonic at the 12th fret.......

...one that's a little more advanced than this one:
 
I doubt that I can mod this.

I don't know how much they cost, I've just always had access to some really nice HP gear through family or work..