If you're a guy, I'm sure every once in a while you've gotten lost but havent asked for directions and thought that you should rather get a GPS. If you are a girl, you probably have thought of getting a GPS everytime you hit the road. Now comes the hard part of deciding on one and getting the most bang-for-the-buck. Let me outline my research and findings to help you get through all the tons of reviews.
Well to start with, a car dealer would love to sell you a "Satellite linked Navigation system" for around $2000. Well the problems are:
a. It costs too much.
b. Its useless when you actually make a air-trip and rent a car in some other city.
c. You cannot use it in your other car.
d. You can buy 3 GPS systems for that money.

Then you have the  All-in-One boxes by Garmin or TomTom or Magellan or Lowrance. At the time of writing this guide they range from $450-1000 depending on memory/accessories included or not and features. When I wanted to buy one, I found them to be around $600 with memory card and car accessories and all North America maps unlocked. Some examples are TomTom Go , Garmin StreetPilot 2620.
The problems I found with these were:
a.  they were too bulky to walk with, if you ever wanted to.
b.  Many of these kind always  need  to be plugged in to the cigarette lighter  power  source, which  meant I had to wire my motorcycle to mount one.
c. Also, they do not integrate with MS Outlook addresses, if you are the kind who has all his/her contact addresses stored and sync-ed in MS outlook.
d. Some of their screens are not as scrollable as dragging around a map with your finger tip. 2 yrs. ago, I found the StreetPilot III to be too expensive and hard to use.

The third option is, turning your existing or new PDA (Pocket PC or Palm) or SmartPhone into a GPS device. I picked this option, because, I could buy a good PDA like Axim or iPaq or Palm   and buy GPS CompactFlash or bluetooth receiver and software and memory card and I was on my way. I bought a HaiCom CF receiver  which would go beautifully with my Axim either in the CF slot. You could also buy a Bluetooth Receiver if your PDA is bluetooth capable. If you want to go cheaper you could get a Mouse GPS receiver but it gives a lot of wire-clutter in the car. For the software, there are many choices. the good ones are TomTom navigator , CoPilot Live , Destinator and OnCourse Navigator . CoPilot is about $100 more than the others. I personally have Destinator but I would like to have OnCourse Navigator. Most of the above softwares have scrollable maps and Outlook integration. I would write reviews of these software separately. Briefly,
TomTom also has a Palm version too.
Destinator has a Motorcycle and pedestrian navigation option. It also has a SmartPhone version.
OnCourse Navigator can take voice commands and can store all North America in about 1GB . Detour option is cool.
Garmin had released iQue which is a Palm PDA with GPS integrated. Garmin's MapSource has a cool desktop software that tracks all your travelled path son the map.
I picked the PDA option because:
a. I could use it with my cars and motorcycle and rental cars.
b. Integrated with outlook addresses.
c. I could walk with it if I was walking in Manhattan or San Francisco or any other city.
d. I can buy/download topographical software and still use the same hardware for hiking etc.
e. In the car, I can keep the receiver (in Bluetooth mode) in a good reception area(like near windshield or roof top) and keep the display device (PDA away from direct sun or lighted area)
f. Upgrading the receiver from a 12 satellite on to a 20 or 32 will only cost me $100. If I want to get newer or better software with new maps, it will be only $100.  Or if I  just want to upgrade my PDA, thats easy too.  Modular is the Key.

 I bought all my GPS stuff from this BuyGPSNow store. I am not affiliated with this store at all.
You could get a PDA for around $200, Receiver for around $100, Software for around $100-140, memory card from $25-$50 (256MB - 1GB SD Card ). Total would be around $450-500.

I have additionally bought a car-mount for my other car and a motorcycle mount for the bike. I love it. Good luck.

Added 06/09/2006:
When I made my purchases 3+ yrs. ago, I did the best I could. But now with the introduction of low-cost all-in-one GPS boxes like the Garmin c330 , Garmin StreetPilot i5 and many other sub-$400 systems, I would recommend you to look at those options too. I cannot write about those, since I have not used any of those.