Killer Sudoku (aka sum doku) is where it's at. It's like a regular soduku puzzle with the normal nine 3x3 blocks, but overlaid on that there are also irregular blocks with a given sum total.

Since numbers can't repeat, some irregular blocks are easy to solve. For example, a 2x1 block with a sum of 3 has to have a 1 and a 2; there are no other options. Same with a 2x1 block with a sum of 17. Can't be anything but an 8 and a 9. From there, you just apply normal sudoku logic to figure out where exactly those numbers are.