I've just finished implementing an interactive marine forecast map at http://www.geoffschultz.org/marine_forecast_map.php. You can click anywhere on the map (over water) and a new window will appear showing you the forecast for that position. I've also added links to all of my logs which take you to a forecast for that location.
The data for this forecast was provided for free by World Weather Online. Note that I've seen large discrepancies between their forecast and other sources, so take it as a simple datapoint and use your own judgement to determine its accuracy.
There was lots of learning involved here...Javascript, XML, JSON. It's been fun! I'm not happy with the data and will probably do a mashup of multiple data feeds to get better results.
-- Geoff