Navionics FishnChip SD card
 

I have one extra of these. It is the Jan-06 USA-East fish chip from Navionics. I know it works in Lowrance GPS units, but I think it works in other brands as well - check their website. To get these you have to buy one of their other navigation chips and fill in a rebate card, etc.

If you haven't seen one, the detail is simply amazing. These are for finding structure. Its like looking at a topo map for the sea floor, way more detail than the info on the regular Navionics chips or the chips for Garmin.

$50, I'll cover shipping unless nearby to central CT.