There are different types of navigation units. It is up to you as far as brand and all. It's probably best to go to an audio store and look at whats available. Most navigation units out right now have a separate "brain". Do you prefer an all in one unit where the navigation is built in to the unit? If you do, I think there is only one unit out that has that right now, and its the Pioneer. Not sure though, as another company may have come out with an all in one unit as well.
The factory model from OEMvalue might fit the '97 but you will have to modify your dash to get it to work properly due to the width of the unit. Here's a link to a thread where a guy did just that.
Pioneer makes the AVIC-N1 which is supposed to be a decent unit and Eclipse offers the AVN line (ie. 2454) which is an all-in-one unit very similar to the Toyota/Lexus factory NAV. Both are pricey.