You might want to look at the Lowrance LMS520C , has external (puck) antenna for the GPS for marking those hot spots (and just as important those dangerous navigation points/places)
I bought one a few months ago and am very impressed , you can download the "emulator" here so you can see how it works (and "try before you buy others as well) even before you buy it. Not "cheap" but not top $$$ the color is impressive on how well detail and differences show up compared to b&w IMO
Emulator(s) here : (NOTE they will not work with MS VISTA OS)
http://www.lowrance.com/en/Downloads/Product-Emulators/
The hummingbird Side Imaging look impressive too, but are much more expensive from what I've found