I don't know much about the ISD line (worked with it YEARS ago but you
can't even find documentation for the parts I still have lying around).

What we have used for our quick-n-dirty demos here at work has been
the Quardravox line of chips. They are controlled by a standard
1-wore serial interface, have very long recording times for all sorts
of interesting sounds, and use .MP3 sound format so you get really
high-quality sound from them.

The downside is that they are rather pricey. Probably not something
you would put into the tagger itself, but maybe a good fit for talking
targets, waypoints, props, etc.