For Germany:

Doctari is the one, I worked with. I can say, they do not always reply on my emails or calls, which I find a bit annoying, but for the rest they are very quick and friendly.

Honorararzt.de is a bit more complex to apply to and register online, but they immediately called me on my mobile to talk.

 

For the Netherlands:

MediGo offers short term jobs for med students and recently graduated. They have an email alert for new positions.