Useful free or low cost solutions
Turn you laptop into a chartplotter with openCPN
Runs on Windows and Mac, easy to install and operate with an easy installed USB GPS see below. Has Waypoints, Routing and more. Even AIS and Radar connectivity and an automated logbook plugin..
All you need is some charts, available for the UK at about £99.
There are a few options which I have tested with OpenCPN. I currently use a USB GPS Dongle which you can find at Maplin.
This works very well above and below decks and the combination makes a very good back-up chart plotter and route planning option.
There is also the the USGlobalsat ND100S and BU-353-W
A cheep option for AIS is to use a Radar Gadgets AIS receiver at £99 which works on Mac and PC through a USB/Serial Port.
I currently have unit which is working through my laptop but needs a better arial option. Suggestion welcome.