For holland the area around rotterdam is not the best bikeing roads but the good news is holland is small and you can get to the good roads very quickly. You have a few options, head east towards germany and around the venlo area (about an hour - hour and a halfs ride) there are some really nice roads around there, from there you can also nip into germany and you are only an hour away from the nurburgring and the beautiful roads surrounding that.
the other option is to head up north towards the islands area there are really nice roads around there and of course you have the massively long dam which is well worth a drive over (no corners but a very very long streight surrounded by sea:) ) if you come up the northern way as i am in amsterdam i am sure i can persuede the missus to let me go out for a ride and show you the roads and teach you to skin up properly(and maybe let you crash in our spare room but you will have to wait till this evening till i sound her out about that and tell her you are an old friend
. (it will take you 1 hour from rotterdam to amsterdam)
As for belgium i just asked a mate from antwerp and as i expected he says stay away from the northern part of the country for good riding, the road surface is shit (you will see what i mean when you cross the dutch/belgian border). The recomendation here is to head to the ardennes area where there are some really nice roads like the N4
http://www.e411-e25.be/01.cfm?lang=nl&expCal=1&expRech=1 but i think thats probably a bit out of your way but the advantge of doing this is that you can cross over to luxembourg then into germany then back into holland if you fancy a longish but very nice ride.
I am checking with a friend if there are any meets or tack days on in holland for the weekend too
