The top three would be Garmin, TomTom, and Magellan.
I have a Magellan 3100 that I picked up for $200on sale; I think it's usually $300. I don't have any complaints about this product. It does it's job, and it's very easy to use.
Most of the entry-level GPS units do the same thing. What you want to look for is POI (points of interest). These are pre-selected destinations that are put into your GPS unit in case you want to search for the nearest gas station, hotel, etc. My Magellan 3100 has only 750K POI's. This is low compared to other models and brands which usually have over 1 million.
If you want to pay a bit more, you can get a gps unit that speaks the street names instead of just saying "turn left ahead." Other cool units you may want are bluetooth, and traffic alerts.