I have a Garmin nüvi 500 and it does the trick for me. One of the things I needed was turn by turn directions so my wife could use it to get to places. Despite her manifold exemplary qualities, she remains slightly challenged at knowing where she is and how to get here or there. The 500 does this quite well.
It is also Geocache enabled. I can upload a gpx file straight from GSAK. I have a polygon filter for my caching area. Currently there are just under 1000 caches in this filter, so that works well. Over 1000 caches gets a bit sluggish. As of 01/01/2010, The nüvi 500 and 550 are the only car devices that support Geocaching. Hopefully this will change in the near future. I would like to have a larger screen.
You can also use a micro SD card with the device, but I have not had great results with that. It seems to not read the gpx on the card if you have a file in memory. I guess if I really needed to use a card, I would figure it out, but syncing it with a cable works the best for me. You get a new drive in windows and all you need to do is export the gpx from GSAK to that new drive (F:\Garmin\GPX\Geocaches.gpx for me) and voila! You are ready for caching.
You can view the caches as you drive along. You tap the screen and it goes into explore mode. You can then drag it around and look at caches below 1.2 mile zoom level. After that, they disappear in explore mode. In navigation mode, you can see all caches up to about the 60 mile zoom level. It is too cluttered at that zoom anyways.
You can select a cache and make it your destination. A little blue cache icon then appears on the side and if you select it, you get the cache details as well as the last 7 logs. You can also see the hint if one is provided. It will also list any trackables in the cache.
The nüvi 500 also supports Wherigo caching, but there are not a whole lot of these caches out there. The whole Wherigo platform is really under developed and buggy. I have not had very good results with Werigos.
There are four Usage Modes to choose from. Driving, Walking, Bicycling and Scootering. I will switch to walking when I am hiking or when I drive within 500 ft. of GZ so I can get in off road mode and see my position where I really am and not stuck to a road. This is only an issue when a cache is close to a road.
You can tell if a Garmin unit is cache enabled if there is a "Geocaches" icon in the "Where To?" menu. Also, on the Garmin website, it will tell you if a certain model supports paperless Geocaching.
The display shows elevation lines and that is really helpful when you are bush whacking and need to find the best approach to a cache. It does not display your altitude in the navigation screen, but you can get to it under Tools > Where Am I?
One of the great things about this unit is that I can quickly locate places of interest like restaurants, gas stations and hospitals. Once you select a location, it gives you address and phone information. This is great for trips and finding hotels down the road or making reservations at restaurants 50 miles out. That saves a lot of time. I even use this when I can't decide where I want to eat. I just pull up the list of Food POIs and scroll down till I find one that sounds good. It lists them by distance from my location and gives me a bearing as well. That way I can tell if I have already passed the place without jumping to the map.
The biggest drawback for me is the battery. It uses a Rechargeable Li-ion battery (Part Number: 010-11143-00) instead of two or three AAAs. This is an issue when I go on all day hikes or cache events. If I don't have access to a power supply to recharge, then I am dead in about two - three hours. The only other thing that I experienced is the loss of the weather cap for the mini-USB connection port. I think I had it for about two days before the flexible plastic cap just fell out during use. No doubt a squirrel is using it as a chew toy now.
The nüvi 500 certainly lack some of the features of the Colorado, Oregon and Dakota series, but it is a cost effective solution for the kind of caching I enjoy. It works great for me! Out of 5 stars, I give it 4 for driving and 4½ for Paperless Geocaching.
You can get the Owners Manual here for more information.