As I don't have the time and energy to maintain a catalogue of links, in the fluid landscape of internet, I'll just give a few that I like, and let you search on from there. Good Luck!

The battle of Norway

Norway during WW2
A good looking Norwegian site with nice photo material and good articles about various aspects of the campaign. They also have a good and active online discussion forum. Something that I'm very envious of!

Norwegian coastal fortresses
A well researched site with material about the Norwegian coastal fortresses and the actions they were involved in at the German invasion.

Norwegian Gloster Gladiators
Another well researched and interesting site for you armchair pilots. It covers the adventures of the Norwegian Gloster Gladiators and their pilots.

Luftwaffe in Norway
An ambitious site, mainly about the German air force in Norway.

Memories and autobiographies

Under the Swastika
The Life of a Norwegian Student during World War II as told by Olav Brakstad.

General Dietls diary
The diary of the commander of the German force in Narvik during the period 5.April to 9.Juni, translated to Norwegian. 

World War 2 in general

German Armed Forces
A great site for all kinds of info about the German armed forces. Very ambitious and professional.

Norway in general

Norwegian geographical department (Kartverket)
They have a useful map service, norgeglasset, that allows you to look at detailed (though small) maps of any part of Norway.