If normal Sudoku’s are boring for you than you must visit this French website with Giant Sudoku’s. The site is in French but that shouldn’t be a problem as the numbers in French are the same as in English.
You will find Giant Sudoku’s in several sizes : 16×16, 25×25, 36×36, 49×49, 64×64, 81×81 and 100×100, so Sudoku’s with grids from 256 to 10000 cells. A new set of grids is proposed every week.
As far as I could see it was not possible to play online or easy to print the Sudoku’s, hopefully that will change soon.
Check out many other Sudoku variants. Happy Puzzling!