>         I've had great luck with 16 MHz ceramic resonators with built-in
> capacitors from muRata.  I'm using them on a 16c74a.  We've probably
> shipped a thousand units now with absolutely no problem.  I did find that
> the resonators from Integrity Technology and ECS do not seem to work
> reliably with the PIC (at least the ones with internal capacitors).  They
> may work fine at lower frequencies or with other chips.

I've found the DigiKey resonators (ECS I think) to work great at 4MHz and
10MHz and not at all at 20MHz.  Haven't tried other frequencies; any idea
what the problem at 20MHz is?