The world today seems awash in 'standard' Sudoku's, whether crammed beside crosswords in newspapers as mentioned, in fat books on the newstands, etc. Yes, they provide a fair degree of logical challenge but in my book have essentially become 'oh-so-repetitive'...once you master the basics, the rest never really changes. While I'd hate to see perlexus ever reduced to just another Sudoku site, as Brian mentions, there really have been numerous new, creative and very challenging logic(and not necessarily mathematically)-based Sudoku-like problems posted here by many contributors. All of which do provide a fresh new challenge and spin on what really has been reduced to, in my mind, an everyday mundane puzzle form.

That said, for a real eye-opener, any fan of this genre should really check out the following site (which appears to originate in Germany, but all the puzzles here are in English):

http://www.sachsentext.de/en/

There are literally hundreds of really neat Sudoku variations here organized under scores of different 'themes'. Definitely proof that the number of possible Sudoku puzzle variations are limited only by the human imagination. There's definitely so much puzzle potential in this genre, I don't doubt we'll be seeing ever different variations for years to come, challenging all generations across the world.