In Holland, Zeeland (province on the south coast) and the Waddeneilanden (the islands of the north coast of Holland and Germany) are really good for birdwatching. Both areas have loads of different types of waterfowl, waders, seabirds etc. In Zeeland there are also quite a few types of birds of prey, including ospreys and falcons.
If you don't mind getting a bit muddy and looking ridiculous, 'wadlopen' (wad walking) is a really good way to see the fascinating Wadden area. Guides take people out over the exposed sea bed of the Waddenzee in low tide to see the unique fauna and flora which the Wadden provides:
Wadloopcentrum Fryslân - Waddling
(English)
I did it last autumn with school and really enjoyed it, eventhough it ended up as one masive mudfight (well... we were schoolkids
) it was one of the most fascinating landscapes I've been in.