Here are links to some useful web pages.

antikvariat.net

Search books in all of Scandinavia. This is a unique collaboration between all antiquarian bookshops in Scandinavia who are members of that country's antiquarian bookseller's association.

vialibri.net

Search books in the whole world. This is in our opinion the best page for uniting different databases of books. The only drawback is the inclusion of Amazon, their prices are based on the number of searches and leads to unrealistic prices on some items.

oria.no

Oria is a search engine for academic Norwegian libraries' resources, books, articles, magazines, music, films and electronic resources, etc.