I agree with
Claymar that marine electronics can be a personal preference.
That said... at a minimum I would recommend a good GPS/chartplotter, a sounder/fishfinder, and a quality VHF radio with matching quality antenna.
Whether you go with a combo unit (combining chartplotter and sounder, for instance), will depend on how you intend to use your boat, how much room you have at your helm, and how much you want to spend.
I went with seperate units on my boat because I had the room to do so, and because I wanted the maximum screen sizes for both my chartplotter and my fish finder.
Placement was also a factor for me. I wear progressive lense glasses, so I wanted all of my critical information where I could see it through the proper portion of my glasses. In addition, the plotter and sounder are positioned where I can see them from the cockpit driving station. The sounder is particularly critical in this respect, especially when drift fishing.
The VHF is mounted directly under the binnicle, with the microphone easilly within reach while in the driving position.
Now comes the 'personal preference part'...
This is what you see in the photo above:
GPS/chartplotter - Garmin 2010c with Bluechart and Bathy chips
Sounder - Furuno FCV600L with an Airmar 'tilted element' thru-hull transducer
VHF - Icom 502 connected to an 8' Digital VHF antenna and an Icom 'Command Mic' in the cockpit at the rear driving station
Backup VHF - Uniden 'Voyager' handheld (stays in the charger and on Ch 16)
All electronics sourced from Jim Maier at
BOE Marine in Annapolis.
http://www.byownerelectronics.com/store/home.php
866-735-5926 (toll free)