Random Adventure Generator

ThemeRevenge
In this adventure, some villain has so offended one or more of the characters that he cannot be suffered to live. (Alternatively, the injured party could hire the characters to avenge his honor.) The villain must be found or otherwise gotten at, setting up the final duel or showdown between villain and 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 HookBetter Late than Never
Some bad guys have arrived and done some bad guy things. The PCs were none the wiser. The bad guys have now made good their escape, and the PCs have caught wind of it in time to chase them down before they make it back to their lair, their home nation, behind enemy lines, etc.
PlotAccumulation of Elements
In this sort of plot, the heroes have to go from place to place -- perhaps covering very little area like a city, perhaps roaming the known world -- and accumulate elements to be used against the Master Villain. These elements may be clues, pieces of an artifact, evidence, or allies.
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 SettingTorturous Terrain
The adventure takes place in some sort of unsettled, uncivilized, dangerous terrain; in action stories, the desert and jungle work best; choose one of those two or decide on a setting that is similarly dangerous and exotic.
Specific Setting IMadman's Fortress
This is the citadel of a major enemy: Strong, unassailable, filled with soldiers and monsters, lined with secret passages and deathtraps; not a wholesome place for adventurers to spend their time.
Specific Setting IICatacombs
These can be catacombs beneath a living city or a ruined one; they can be long-forgotten or still in use.
Master VillainZealot
This villain is like the Conqueror, but he's not trying to conquer to own; he's trying to purge the world of something he feels is pure evil (another religion, a human, demi-human, or nonhuman race of sentient beings, a custom). He operates just like the Conqueror, enslaving or killing all those who belong to the "wrong" race or philosophy.
Minor Villain IInquisitor
This villain is the one who interrogates the heroes and NPCs captured by the villains. He accompanies the other Minor Villain out into the field and works on anyone captured; he enjoys inflicting pain and suffering.
Minor Villain IIMoronic Muscleman
This fellow is a huge, powerful monster of a fighter. His job is to smash anything the villain tells him to smash. He does that very well, but don't ask him to do any thinking; he has no time for such brainy stuff.
Ally/NeutralCongenial Madman
This fellow is a pleasant, happy lunatic whom the heroes encounter; after the initial encounter, he follows them wherever they go, commenting on their plans, behaving strangely, getting underfoot, and -- very occassionally -- proving to be a real help.
Monster EncounterPowerful Tester
Here, some powerful, intelligent monster with shapechanging ability turns into a human form. When the heroes encounter him, he is in need of help or having trouble. He also obviously can't reward the heroes for their help, and will only serve to slow the heroes down from their quest. If the heroes help him anyway, the Powerful Tester reveals himself in his true form and offers to aid the heroes in their quest.
Character EncounterBureaucrat
Some time in their adventure, the heroes must deal with the local government and run into that most horrible of nuisance monsters, the bureaucrat and his red-tape dispenser. The heroes don't have the right forms. When they have the right forms, they forgot to fill them out in triplicate. And so on.
DeathtrapAvalanche
This is an outdoors trap. Some time when the heroes are in a narrow canyon or gorge, or are on a snow-covered mountain, their enemies can arrange to dump an avalanche upon them (rocks and boulders in the first instance, snow in the second).
ChaseSpecial Terrain
You can make any chase more memorable by having it take place in a setting to which it is utterly unsuited. For instance, horse chases are fine and dramatic when they take place through the forest, out in the open plains, or along a road -- but they become diabolical when they take place inside the Royal Palace or in dangerous, labrynthine, treacherous catacombs.
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 WeaknessHoly Symbol
The villain may have the traditional weakness to a specific holy symbol -- but don't choose just an ordinary one. It may be a holly symbol no longer used by the church, or may be some forgotten variation of the current symbol. (For instance, the cross may not work, but a variation -- such as the Roman cross -- might; alternatively, it might have to be a holy symbol which has undergone some unfamiliar ritual.)
Special ConditionMagic Doesn't Work Right
If the adventure is taking place on an alternate plane, then that plane's magic works oddly or not at all. (A spellcaster will find that just making himself useful is a challenge when none of his spells works.)
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 HerringLoony who Has It Wrong
You can have the heroes "aided" by a so-called expert who is actually a lunatic who doesn't know anything about what he's talking about. Once he's led the heroes off to some remote part of the continent, his evasive answers and bizarre behaviour will alert them that he really doesn't know anything about what he's pretended to be an expert on.
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.