Random Adventure Generator

ThemeHorror
This type of adventure is designed to scare both the characters and the players. Just having a monster attack is not enough for a horror theme; the monster must first frighten the characters.
GoalSurvive Environment
The characters could end up in a hostile environment which they must cross -- a desert, a jungle, or other hostile setting. In the course of the adventure they'll need to find food and water, resist the elements, and perhaps fight off attacks of the natives.
Story HookHero Offended
Someone greatly offends the hero, so much so that he'll pursue his offender right into the adventure. (Note that this usually means that the offender is a minion of the Master Villain. You'll have to decide whether the minion offended the hero precisely to bring him into the adventure or just as a side-effect of his ordinary villain activities.)
PlotA-B-C Quest
This is an epic sort of plot. In it, the heros are given (or undertake) a task to perform: The taking of a city, the rescue of an innocent, the destruction of a monster, the creation of a magical item, the defeat of a Master Villain, etc. But the path to victory is not a simple one. To get to their goal, Event A, they find that they must first accomplish some other task -- Event B. But when they undertake the task of accomplishing Event B, they find that they must first accomplish Event C. This goes on for several encounters, until the heroes accomplish all the obstacle events which prevent them from returning to Event A, their original goal.
ClimaxScattered Duels
In this climax, the heroes have gotten to the end of their quest -- they may have broken into, sneaked into, or escaped from imprisonment within the villain's citadel, or have marched into the little town where the villain is holed up -- and they become separated. You can separate them by having traps and tricks break the party apart, by having them see two or three things they must resolve (such as danger to innocents or the appearance of minion villains) pop up simultaneously; they'll have to run in all directions at the same time or suffer failure. Once the party is broken down into bite-sized chunks, you confront each individual or small group with the enemy or enemies he most deserves to face -- his personal enemy, the monster which defeated him before, etc. -- for a grand series of climactic duels.
General SettingOn the Road
Most of the adventure takes place on the road, as the heroes are travelling from place to place. This is especially good for adventures where heroes are investigating a wide-ranging mystery, are part of a caravan, or are being pursued by loathesome villains.
Specific Setting ICatacombs
These can be catacombs beneath a living city or a ruined one; they can be long-forgotten or still in use.
Specific Setting IIMagical Lake
This is the acquatic equivalent of the Legendary Forest, here beautiful and glistening, there treacherous and dangerous, filled with water-breathing magical folk.
Master VillainConqueror
This character is moving his army in to take over; that's what he lives for. He's been the enemy of your characters' nation's ruler, and has launched a full-scale invasion of your characters' favorite nation. The heroes have to beat their way through or elude his hordes of soldiers in order to get at him; better yet, they might lead their own nation's troops against his and outthink him in military fashion.
Minor Villain ISingle-Minded Soldier
This most trustworthy of villain minions is the experienced, competent, persistent soldier -- a field-trained officer who serves the villain with military precision. He is usually encountered in the field as leader of the villain's field operations. He is not encountered directly until the middle of or the latter part of the adventure; until then, the heroes encounter only his subordinates.
Minor Villain IISingle-Minded Soldier
This most trustworthy of villain minions is the experienced, competent, persistent soldier -- a field-trained officer who serves the villain with military precision. He is usually encountered in the field as leader of the villain's field operations. He is not encountered directly until the middle of or the latter part of the adventure; until then, the heroes encounter only his subordinates.
Ally/NeutralArrogant Snob
For some reason, the heroes have to accompany or escort an arrogant nobleman or craftsmaster. They can't afford to abandon or kill this person; he or she may be their employer, an expert on the place they're going to, one of their relatives, or a relative of the royal family. And this person makes their life hell with sniping comments, haughtiness, and other unbearable traits.
Monster EncounterNocturnal Predator
This is a classic monster encounter; the arrival of a hungry carnivore in the middle of the night. Usually, this attack happens to heroes camping between villages or out in the deep wilderness; a wild animal, attracted by food odors (from the heroes' campfire or from the heroes themselves) sneaks in for a bite.
Character EncounterNew Enemy
In the course of his ordinary activies, one of the heroes can make a New Enemy. Hurrying along the street, he can bump into a disagreeable fighter for whom an apology isn't enough; in a tavern, he can make some innocuous remark that you deliberately have the irritable fellow misconstrue as an insult. The New Enemy will only exchange heated words with the hero at this point, but will appear again later in the adventure and will eventually have to fight the hero.
DeathtrapRock and a Hard Place
This trap starts out as an Animal Pit, Pit and the Pendulum, or Tomb Deathtrap, but an obvious escape suggests itself very early on. Trouble is, it leads into even worse danger. The hole out of the animal pit may lead to the lair of an even worse animal; it may lead through a succession of dangers (collapsing old catacombs, into an underground river, into a den of zombies) before the heroes reach the light.
ChaseAerial
The heroes could be riding pegasi or friendly griffons or allied great eagles; the villains could be carried aloft by gargoyles or demons. The prospect of taking a mile-long fall if one's mount is hit is a very daunting and challenging one for the hero.
Omen/ProphesyHero Fulfills Prophecy
This is the most useful sort of prophecy. In the early part of the adventure, one of the heroes discovers that he fulfills some ancient prophecy.
Secret WeaknessElement
The Master Villain can be banished, dispelled, killed, or otherwise defeated by some of element or item. The Master Villain tries to get rid of all the examples of this element in his vicinity; he doesn't let his minions carry it or bring it into his presence. But he's not stupid; he doesn't announce to the world what his weakness is. He tries to hide his concern within another command. If he's allergic to red roses, for instance, he orders all "things of beauty" destroyed within miles of his abode.
Special ConditionTime Limit
Finally, the most obvious condition to place on an adventure is to give it a time limit. If the Master Villain is going to conclude his evil spell in only three days, and his citadel is three hard days' riding away, then the heroes are going to be on the go all throughout the adventure -- with little time to rest, plan, gather allies, or anything except get to where they're going.
Moral QuandryHonor Quandry
You want to use this on the character with the most strongly developed sense of personal honor -- someone who has lived all his life by a strict code. Toward the end of the adventure, this character realizes that the best way to defeat the Master Villain is a violation of that code. For instance, the character might be a paladin, who discovers that the only possible way for the heroes to defeat the Master Villain is to sneak up on him and stab him in the back.
Red HerringFalse Path to the Artifact
Once again, if the heroes have had too easy a time finding the artifact capable of destroying the villain, give them trouble this way: When they get to the place where the artifact is supposed to be contained, they find the coffer or chamber or whatever empty, obviously looted by robbers, who have scrawled such remarks as "Kelrog was here!" upon the walls.
Cruel TrickWanted by the Law
One final complication, one which occurs pretty frequently, is when the heroes are wanted by the law. When they're wanted by the law, they have to travel in secret and very limited in the resources they can acquire.

Based upon tables from the Dungeon Master's Design Kit by TSR, Inc.