Online tournaments:
http://logicmastersindia.com - Indian online sudoku and logical tournament every month. Authors from all over the world
http://www.fed-sudoku.eu - every day online sudoku
http://www.puzzleduel.club - every day a new puzzle
https://sudokumaniacs.com/ - A handcrafted Classic Sudoku and a handcrafted Variant Sudoku every day, with online solving.
http://www.argio-logic.net/ - Italian online tournament every week, Roulette, Contest, Classic only Contest, Hybrids and Headshrinker
http://www.puzzlefountain.com/ - almost every week online tournaments with logical puzzles, occasionally also sudoku tournaments
http://www.e-sudoku.fr/ - French web site with online classic sudoku
http://croco-puzzle.com/ - German online logical puzzles every day
http://killersudokuonline.com/ - online source of killer sudoku puzzles
http://kwontomloop.com/ - every day source of Slither link puzzles
http://www.speedsudoku.com - speed sudoku for 2-8 players
http://cs.sudokucup.com/ - Czech online sudoku tournament - twice a year
http://forsmarts.com - logic games and puzzles by V. Portugalov
http://www.puzzleup.com/ - Turkish online logical puzzles tournament
Related pages:
http://www.conceptispuzzles.com/
http://motris.livejournal.com - Thomas Snyder’s blog
http://valezius.blogspot.com - Zoltán Horváth’s blog
http://www.ukpuzzles.org/ - Official web page of the UK puzzle association