For the longer term forecast I typically take a look at the Sembach loop to get the general synopsis.
21st Operational Weather Squadron
I then use the Wetterzentrale to look at the diagrams for the area(s) I'm going to fly in (see diagramme; GFS 0.5 degrees) and if necessary also the Bracknell and EWS models (see FAX) to see if there's a discrepancy between them and Sembach. Note that there's an error in the logic of the Wetterzentrale that downloads the Sembach, Bracknell and EWS synopsis charts: you need to look at the forecast date, but also the production date to see if the Wetterzentrale really grabbed the correct and full set. It happens regularly that you are presented with 2004 data, or that the Bracknell series is a mix of the 0000Z and 0600Z runs.
Wetter : Wetterzentrale : Top Karten
Closer to the date, the TAF and METAR from any source available. For a long-distance flight I find Met'map very useful since it gives a color-coding of all airfields over a larger region, so you know where the trouble spots are, and can zoom in as necessary.
MET'MAP - ORBIFLY FLIGHT SCHOOL - IFR ET CPL AMERICAIN EN EUROPE - FAA IFR AND CPL IN EUROPE
Further, Meteox (or its Dutch equivalent Buienradar) is useful for those short local flights just before or after a front passage.
Meteo Weather Meteox.co.uk - Weather - European rainfall radar
Upper winds are contained in the Low Level Forecast for the Netherlands. For the UK I would use the 415/416 forms and other countries present that info generally in different forms as well. My preferred stop for that kind of information is Luchtvaartmeteo.nl but that's only for Dutch pilots (have to fax or e-mail a copy your license to get an ID, or be a registered member of one of the Dutch aviation organizations.)
https://www.luchtvaartmeteo.nl/
In-flight of course there's VOLMET, ATIS and if it's not too busy any ATC frequency is happy to give you the weather for any location you need.
As an aside: I was flying back as passenger from Milan to Amsterdam last week, but had a private flight planned in the evening. I asked the cabin crew if they could ask the flight deck to print the TAF for Rotterdam for me. About 10 minutes later the captain brought the ACARS-printout to my seat personally. Nice service!