I thought that I might highlight a couple sites that focus on sudoku variations. The first is djape.net whose specialty is overlapping sudokus. These puzzles consist of more than one sudoku board that overlap so that you need to solve one in order to get the clues you need to solve another. Some of the more recent interesting variations include a “flower” sudoku with overlapping “petals” and a 9+1 clueless sudoku, where the middle squares of the nine form the tenth sudoku which initially contains no clues.
The other site I would like to mention is SuDokuPlace, which is a good place to find jigsaw sudokus and sudokus with non-standard grid sizes. There is a section dedicated to puzzles called SuDozen a 12X12 grid sudoku.
