Anydice is an online probability calculator. Useful for game and rules designers.
probabilities
Probabilities of Odd Dice Combinations
Gnome Stew has an interesting article on the probabilities of various polyhedral dice.
Dice Probabilities Article
I don’t know of a miniatures wargamer who hasn’t tried to write his own set of rules. And unless your rules are extraordinarly simple, that means thinking about dice probabilities. Here’s an article on die probabilities with d6s, with a special focus on DBA and Warmaster.