There are many choices these days for GPS portable navigation devices, and you really need to know what features you want and or like in a GPS before you start looking into buying one.
You need to do as much research online as possible and than go visit a local GPS retailer to test the unit you may consider to purchase.
Some features that are very popular and high in demands are
Text to speech where it pronounces the street names when giving verbal directions.
You would want a larger display like a 4.3" compare to a 3.5" display if possible
Do you need hands free Bluetooth capability for hand free calling?
Do you need map of NA including Canada or just 48 States?
Do you need real time traffic service?
How much Points of Interest information do you need or wish to have? Points of interest contains name and address of restaurants, gas stations, hotels, airports etc to make your navigating experience much more enjoyable. Don't have to look up addresses for a restaurant if you need to find one near you or across town. Normally, most will have between 1 million POI to 6 millions POI, the better unit have between 4.5M to 6M POI's.
With that said, I would recommend for you to look at possibly 3 popular GPS manufacturers.
Garmin is currently the North America leader in GPS products, Consider the new Garmin Nuvi 265W which is not yet available till late Sept this year, This unit will offer you pretty much everything at a $299 price point.
Currently, best deal going for Garmin products is the NOH Garmin Nuvi 760 at $329 offered at Auto Nav 2000 Plus, Inc. which is an excellent deal for a unit that normally sells for $499.
http://www.autonav2000.com/mall/anProdDetail.asp?ProdID=808
The Nuvi 760 is a full feature GPS that includes TTS, BT, Traffic, 6M POI's, Travel kit, MP3 music etc, just about everything Garmin has to offer currently except the voice input that is found on the Nuvi 850/880, they cost $799 / $899 and personal that is a huge price difference for one extra feature.
Next, I would consider the TomTom GO 730 at $399 or the TomTom Go 330-S.at only $299. Both have text to speech, full NA mapping software at a very reasonable price.
http://www.autonav2000.com/mall/anProdDetail.asp?ProdID=764
http://www.autonav2000.com/mall/anProdDetail.asp?ProdID=784
Last but not least, consider the Magellan Maestro 4250, it is currently Maestro top of the line and it comes with TTS, BT, TMC, VR, full NA mapping software and tons of POI's.
This unit is being offered for only $299
http://www.autonav2000.com/mall/anProdDetail.asp?ProdID=633
If you have a budget and wish to own a unit that is cheap but effective,
I recommend you to consider the Magellan CrossOverGPS NOH at only $199 and it includes the latest V2 mapping software, TTS and even software for Outdoor hiking, geo-caching along with marine application to be use on a boat. This unit is also water resistant and can be mounted on a motorcycle or bikecycle.
http://www.autonav2000.com/mall/anProdDetail.asp?ProdID=831
You can find GPS unit comparisons on http://www.autonav2000.com/Compare/index.html
If you wish to try a few of these GPS out before buying one, you can rent one from GPS4Rent at http://www.gps4rent.com/
Good luck and hope these information help you make a good decision when purchasing a GPS.