Here are some useful programs, spreadsheets, etc. that you will find useful in your Chainmail games.

D&D Miniatures warband generator

Compiled Dungeons & Dragons Miniatures Errata

Dungeons & Dragons Miniatures FAQ

Dungeon Tiles for D&D Miniatures - Wizard's Study

Chainmail FAQ from Wizards of the Coast

Chainmail Model Tactics from Wizards of the Coast - some of the designers of the game take a closer look at tactics with the Chaimail figures.
Chainmail Warband Generator from Wizards of the Coast - a generator tool for constructing warbands.
Chainmail Warband Record Sheet from Wizards of the Coast - a useful record sheet for planning your warbands.
Chainmail Terrain Cards from Wizards of the Coast - A downloadable form of all of the available terrain cards for Chainmail.

Downloadable Battle Sheets with D&D stats for Chainmail models.