I use the Garmin GPSMAP 172C, purchased at Southampton Boat Show last Year, never let me down, easy to use. It even has tide tables which is nice. I went for the model with the internal GPS aerial as it's on a rib. Easy to take off the boat so it's not nicked (30 secs to remove).
I was going to purchase the next model up with the fish finder etc built in, but then you only get half a screens worth of depth and half a screens width of chart! or one of the other. I think the extra cost of the unit was dearer than buying a seperate Garmin Fish Finder!
Very pleased with the unit - very easy to read in direct sunlight and at an angle. The screen brightness is so good that it doubles as a navigation light when it shines in your face at night (you can turn it down)
Proper nav lights now fitted