Well, there's a lot of variety in GPS. I got a setup from Pharos for my Dell Axim X5 PDA, which can be mounted in the car. That's one thing to consider. I have not yet used it because I needed a Compact Flash card for holding all that data. But I just got one so I anticipate I'll load a bunch on there and see how I can navigate with it.
There are also dedicated GPS units that sit on the dash.
You can spend a little or a lot on them.
My suggestion to you is to shop Amazon, BestBuy and every electronics site that has lots of information to look at the features, functionality and price of these units, decide on one, talk about it on some BB with GPS users to really get a feel for what you've decided on, make sure of your decision, and then shop around for the best price you can get on it.