I recently found a website full of interesting resources for D&D players and Dungeon Masters. Its called ADnD Downloads. But don’t let the name fool you; it covers all versions up to 4E.
Of particular interest to DMs is the Creator System; a free tool designed to help create maps and scenarios for RPGs. There’s some other useful DM tools such as Dice Rollers and some useful condition and effects trackers on the Character Sheet page.
There’s tons of other stuff as well; so have fun exploring.