The manufacturer's website Garmin.
Garmin make several ranges of GPS receiver.
The eTrex range is arguably the most popular. A comparison chart of the models can be found Johnny Appleseed's Comparison Chart.
Garmin symbols can be changed for many models. Instructions can be found here - Geocaching Symbols on a Garmin GPSr
While the following models may be discontinued, it is still quite possible to use them for today's geocaching.
(add more if you want)
There are many free maps available for Garmin GPSrs through Open Mapping Projects