After getting spoiled by the Alpine DVD-based OEM navigation system in my Acura 3.2TL-S, I looked around to see what was available to retrofit into our truck. After a lot of searching, I finally decided on a
Garmin Streetpilot 2620 system in lieu of an aftermarket in-dash replacement system.
This portable system has the added advantage of being usable in Madame Boomer's Durango as well as the truck - in fact, she has appropriated the thing!

It has all of North America programmed into the mapping database which is stored on an internal hard disc, so there are no fees for unlocking additional regions, and transcontinental routes can be mapped as a single route.
We've used the Garmin for about a month now and are very pleased with it. The mapping database is basically the same one used by MapQuest on the Internet and is much more robust than the one in my Acura. It has no problem with obscure addresses in the smallest towns and (to my surprise) even tracked us complete with street addresses as we traveled down some private roads. All in all, it will do everything the OEM system in the Acura will do and more.
Despite its healthy list price, the system is available on the Internet for less than $1,000 - I wound up purchasing ours from 4wheelbooks.com and paid less than $1,000 even with overnight shipping.
Edited to add link to Garmin website with more information.
Rusty