I have just bought a new GPS (on Friday) so i have an opinion

I have owned a few, from some early B&W units with no base maps which were useful in conjunction with a good paper map. I like the Garmins; the Magellan, Tom Tom have inferior mapping and route finding.
I had a car GPS from LG that came free with a fridge, but it was not very good. The route finding was crap, it tried to route me 200 miles out of my way because it thought a 10 mile ferry trip was going to take 8 hours. It died when I plugged the 12v jack from my radar detector into its 5v socket which were both the same size.
I bought a Garmin 60CX a year ago and it's an excellent trail/off road unit. I have given it to my son for that purpose. They have been superseded by newer models, but are an excellent & robust general purpose off-road GPS
After a lot of soul searching I decided on the
Garmin Nuvi 550 This is a cross over car/hike/bike/boat unit. I was leaning towards two seperate units but this looks like it will do everything I need. It's expensive for a car unit ($450), but it is waterproof, with a big battery.
I ordered it on Friday so it should be here next week. I'll give an update when I get it.
This is a new model so it's priced at a premium. Garmin keep bringing out new models and discounting the old ones, so buying last years model saves a bundle
If you only want a car GPS the Garmin Nuvi 260 are really cheap ($125) - Garmin are discounting them by $100 - and pretty good. For a hundred more you can get the Garmin Nuvi 760 with bluetooth hands free phone and wireless traffic updates.
Maps are the hidden expense in GPS units. They are very expensive to buy if your GPS doesn't come with all the ones you want. Of course you can find torrents and key code crackers but that would be illegal. So don't go to ThePirateBay.org and search for Garmin.
E.g. You can buy the Blue Chart Americas CD for $150 - but that doesn't include the key code to actually download the charts to your GPS. Key codes for a particular area can cost $100 or so. If you paid for all the key codes you can rack up thousands of dollars - and those key codes are tied to the individual GPS. If it falls overboard you start again
Now marine charts are unusual since they are expensive anyway, but most US GPS units sold don't have road maps outside the lower 48. If you want Europe (or Mexico or Canada) you'll have to buy extra maps and download them. It might even be cheaper to buy a cheap GPS in Europe than buying a US model and buying the maps.
I want one linked into Google Earth but that's a few years away.