Like the others have said there are many choices to be had depending on your type of travelling. I have moved away from the more traditional tom tom type devices and now use only smart devices, as for our purposes I find them far more versatile. Not only can you get great (and usually very well priced) navigation apps you can add a whole host of other useful apps that in the end give you a far more bang for buck.
At the moment we use a nexus 7 android tablet and a combination of google maps,
osmand,
orux maps can use our oziexplorer maps. As well as other apps like aussie weather radar and
wikicamps. If you are into 4wd trips then have a look at
mudmap, it is a bit expensive but is probably not bad value if you don't already have a lot of maps.
osmand can use maps from the
open street map (OSM) project and allows you to download maps for offline use.
OSM maps while not as complete as some other sources still have a lot to offer. the map data is available free to use and is updated daily so you can always get the most up to date maps they have available. the other thing is if you find data that is not correct or missing you can add the information yourself and everyone will benefit from your work. This feature is also great as a family activity while camping. We are going to an out of the way national park over the easter break and i am hoping to map in some of the walking trails and other poi's using
osmtracker on our nexus 5's.