With access by wifi, and smart phones now common, a huge variety of weather resources are available. Although data costs are dropping rapidly, they can still be an issue (especially over a satellite phone), and if that is the case, there is no real substitute for using data-efficient grib files. But where cost is not an issue, the variety available is bewildering, so here are some of my choices.
The Met Office website has improved beyond all recognition, and once you have found your way round it, it is more than adequate for both passage planning and getting current data for UK and adjacent European waters. It is best to start from the Marine Forecast page, and find your way from there. The gallery above includes some of the features.
Some people also like Weather Online UK. You have to choose a forecast area from the list (e.g. Wight); then select a station (e.g. Cowes), and you can choose a forecast period up to 7 days (or more if you are prepared to pay). This gives a useful tabular presentation. Options also exist to show peak gust, wave height and other parameters. Very useful!
More generally, Passage Weather offers a worldwide view giving charts of wind, pressure and wave height at a variety of scales for about a week ahead. A simplified Android app for Passage weather is available too.