I have published a number of sudoku books with Cappelen Damm:
Sudoku
Explains most solving methods, with puzzles at every difficulty level.
Sudoku 2
The follow-up to Sudoku, with difficulty levels 1-6.
Sudoku-Varianter
Sudoku variants: diagonal, even/odd, irregular boxes, no boxes and combinations.
Junior-Sudoku
Sudoku for kids, ages 6-11+.
Wordoku
Sudoku with letters — with a hidden word in one diagonal.
Killer-Sudoku
A mix of Kakuro and Sudoku. A must for those wanting new challenges.
Kakuro
For those who like numbers. Time to sum.
Hitori
Hitori — sudoku’s little brother. Shade cells so no number repeats in any row or column.