multiple power supplies in a modular

[Mikko Helin]

Tony Clark wrote:
> I tend to use 22 ohms instead.  This gives a cutoff of ~70Hz or so which
> is adequate enough to kill all high frequency garble.

Ingo asked:
>What about using a cheap inductor (100uH or so) instead of a resistor?

I guess small inductor is only good for high frequencies. 

My question:

What is best way to isolate analog and digital power supplies, is
an extra regulator for digital circuits any better than simply
a resistor with bypass cap? 

Mikko