Dungeonslayers is a very well done, old school RPG. The author writes:
Welcome to Dungeonslayers, the role-playing game, in which your characters are slaying monsters and looting dungeons in a primitive and old-fashioned way. The rules of Dungeonslayers were designed to be very basic and simple on purpose, to bring the charm of old-school gaming back to life. Dungeonslayers is not about having elaborate, realistic rule mechanics nor about playing out pseudointellectual dramas filled with egomaniac monologues. Instead it’s about straightforward plots in your traditional fantasy world, where evil is still evil, where monsters are killed mercilessly, where devious traps strike and where fantastic loot awaits, while pencil and graph paper work their own special magic around the gaming table. So, let’s put on the chainmail once again, draw your blade or dig up your spell book, the next dungeon and its monstrous hordes await your return.
The site also has some neat one-page dungeons.