[McGillicuddy]

Regarding extra features the man over board (MOB) is fairly standard now. Granted it has a designed purpose but personally I think its a great feature for fishing. As soon as I get hit on the troll, or mark a big baitball, or good bottom I go right to the MOB button and thus the repeatability of the fishing that zone is again greatly enhanced.

I just got a new Northstar 538 Chartplotter with ext. antenna for $258 from getfeetwet.com because its being discontinued, its only a 4" screen but for fishing that's all I really need. Same tech and features as their $800 units but smaller.

I just saw a Northstar 457, a 5" hi-res screen, dual freq. fish finder for $519 which includes a very good transom mount transducer. That group also has very nice 6" combo units for about $650. Regarding chart cards, the 2 big players are C-map and Navionics... Former partners, and both pioneers in digital mapping, their two owners/founders are constantly trying to improve over the other in a lively and spirited competition. Garmin also has their own Bluecharts, a variation of those, perhaps the improved version Big Lew spoke of. Any one may be short a channel buoy or a shifted bar or obstruction but for the most part they are all pretty impressive. Which is better? Depends on the chart. Additionally they all have various levels of "marketing features".
Be careful with second hand stuff cuz people may not want to remove their antennae or transducers (why fill holes if their new unit is compatible w/ old antennas and transducers and those parts are more expensive when bought w/o unit) Good Luck.