whats the best way?  I mean...im sure its possible.  One idea i thought up is to put it in an LR circuit, and figure out the cutoff frequency (i guess with a computer interface) impedance - inductance - can be figured out from this, no?

would that work, and are there better ways?  

In the lab im working in there's a $10,000 "precision impedance analyzer"  That would probably work :-D

edit: and yes, its 2:30 am, so....dont yell at me.

inductors... possibly you could get some meaningful info out of an RCL bridge.

Transformers... much harder. You might be able to work out the P:S ratio, a frequency cut off can be obtained, you can certainly read the inductance (but that won't tell you anything really), but you'll struggle to find the specs of the core material etc.

Best to have a guess and underate it.

Depends what you want ot do with the transformer, if it is power, then running say 6.3v AC into the thickest wire winding, will give you some (possibly lethal) voltages to check out on the other windings, then it is up to you to decide which of these is the 110 or 230 primary winding. Plus you are on you own to decide whether the insulation will handle the voltage  :shock:
For small audio trannys, the dc resistances are at least an indicator of their purpose.