KenKen
The KenKen Uniqueness Guide
Which combinations are unique for common cell shapes and all operations on a 6x6 grid.
The KenKen Cheat Sheet 2
Which additive combinations are unique for a range of cell shapes for 4x4, 5x5 and 6x6 grids.
KenKen Combinations Finder
A program written in Haskell with front-end written in Multimedia Fusion. Lists possible combinations. See blog post.