Here is my list where you can find solving techniques for sudoku variants ( I skipped vanilla sudoku and killer sudoku because there are many places with these techniques). Remember the techniques of vanilla sudoku apply also in most of the variants. My hope is that other know more such technique pages to complete the list because it is not so easy to find such pages
Sudoku X
http://www.djape.net/sudoku/forum/viewtopic.php?t=237=&start=3 (crossover, double crossover, triple crossover, triangular connection)
http://www.djape.net/sudoku/forum/viewtopic.php?t=344&postdays=0&postorder=asc&start=15 (different techniques)
Non-Consecutive Sudoku
http://www.djape.net/sudoku/forum/viewtopic.php?t=347&start=5 (different techniques)
http://sudoku.apinc.org/?p=139
Jigsaw Sudoku/Cylindrical Sudoku/Toroidal Sudoku
http://forum.enjoysudoku.com/viewtopic.php?t=4257 (law of leftovers, paired pointing pairs)
http://www.sudoku.org.uk/discus/messages/1289/1682.html?1149884395 (generalization of paired pointing pairs)
http://sudoku.apinc.org/?p=107 (law of leftovers)
http://www.bumblebeagle.org/dusumoh/8x8/tutorial/index.html (law of leftovers)
Jigsaw Killer
http://sudoku.apinc.org/?p=109 (law of leftovers for jigsaw killer)
Toroidal Sudoku
http://forum.enjoysudoku.com/viewtopic.php?t=3516&start=15 (repeating numbers)