http://www.killersudokuonline.com/ has daily killers, a weekly killer, a weekly "greater than" (an interesting sudoku variation)... and a "greater than killer" is promised soon.
Not sure if anyone else was aware of this site. Archive contains 30+ puzzles. There is also the option of playing the daily puzzles online, and a neat pop-up window which gives all the permutations for cages of a particular size/total with given includes/excludes.
