Magellan and Garmin are the two big guys to check out. I have an inexpensive Magellan and my friend has a higher end Garmin. We found both to be perform well however the Garmin was slightly more accurate. Typically the more you pay, you'll get more points of interest and other features. For me, I just need the map and basic navigation so something as simple as the Magellan Maestro 3225 does the trick. If you don't mind spending more, check out the Garmin Nuvi 650.

The best for your price range is the Magellan 4250 (300.00 at Costco), which is currently Magellan's top of the line model right now. If you do not care about the features (just want a simple no frills GPS unit), the Garmin nuvi 660 (350.00 at costco) is great (less features than the Magellan but has a SLIGHTLY better routing engine). Hope this helps!