I like the sudokus where you have to mark the odd-even cells. Such as Mathrax or yesterday Odd-Even Count Sudoku by Prasanna Seshadri.
Here is another this kind of sudoku.
Rules for Even Group-Inequility Sudoku:
Follow Sudoku rules. The given inequalities show that which side contain more even digits. Such as the first sign in the second row show that the first 3 cells contain more even digits then the second 3 cells.