I have a Garmin etrx, it can be used by my navigation software, and I can upload waypoints from the PC to it and use it stand alone. Its waterproof and shockproof dont ask how I know.
Cheap but does what it says on the tin.
Only downside is its battery hungry but then I should power it from the boat.
If you only require long/lat the b/w Garmin gps72, but if you want colour hand held plotter either the Garmin gpsmap76Cx or the gpsmap60Cx. Screen small. Option for a portable is the gpsmap276C which is simply the best small plotter on the market by a country mile.