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.
GoalClear Name
The name of one of the characters or an NPC has been sullied and the characters must clear it. The characters must find out a) why the name has been smeared, b) who is responsible, and c) why the responsible party is doing it; then they must find evidence to convince everyone they're telling the truth.
Story HookMissing Memories
One or more of the PCs wakes up with no memory of the recent past, and now they find themselves in some kind of trouble they don't understand. The PCs must find the reason for the memory lapse, and solve any problems they uncover in the meantime.
PlotEvent
For this plot, choose some sort of event -- a tournament, a holiday, a celebration called by the king, a masked ball, or whatever -- and set the commencement of the Master Villain's plan against that backdrop.
ClimaxThrone Room Duel
This is set up much like the Scattered Duels, except that you don't separate the heroes. It's harder to control whom fights who in this situation... but if it doesn't matter who has the final duel with the Master Villain, this is a classic climax choice.
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 IMansion of a Lord
This can be the home of a villain -- the characters may have to break in and rescue someone or steal evidence, or break out if they've been captured -- or of a heroic ally, in which case it may be used as the headquarters for the heroes' plans and activities.
Specific Setting IILaboratory
This can be alchemical lab of a friendly wizard, or the horrible experimental chamber of the villain where new monsters are created and relased upon the world.
Master VillainAdvance Agent
This villain is the vanguard of some sort of invastion; often, he is trying to open up a portal to a dimension full of trapped demons and evil gods.
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 IICoward
This character is an ordinary grunt minion of the Master Villain, but he's a coward. He's deathly afraid of the Villain and the heroes. He's best used when you plan to have the heroes captured; by his mannerisms, you can make it clear to them that this fellow is a coward and they will begin to work on him psychologically.
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 EncounterForeshadowing Monster
With this monster encounter, combat may not be necessary. This monster encounter exists to alert the characters to the fact that something unusual is going on, a foreshadowing of their upcoming conflicts with the Master Villain.
Character EncounterBelligerent Soldier
The billigerent one has just had his ears pinned back by his commanding officer and is anxious to take it out on some hapless civilian. If this is a city gate, he claims that the hero's papers are wrong or that he recognizes the hero from descriptions of a wanted criminal; if this is the streets, he insults the hero's lack of military bearing, pretty looks, clothes, smell, companion, or whatever it takes to provoke a reaction.
DeathtrapDemolition Zone
In this classic deathtrap, the heroes are placed (usually bound and weaponless) in some building or area just as it's due to be destroyed.
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/ProphesyReincarnation
The hero, seeing the portrait of some long-dead nobleman, may be surprised to see his own face staring back at him. All evidence points to the fact that our hero is the reincarnation of this person, and the Master Villain may desire to destroy any trace of that nobleman's existence. Just as appropriately, this long-dead nobleman may have died after making some important choice -- such as choosing love over career or career over friends; and the choice he faced is identical to the one the hero now faces. Will our hero defy the prophecy and choose as he did in a previous life, or will he choose the other option and see what happens?
Secret WeaknessSecret Embarrassment
Finally, the villain may have some aberration or secret shame that will force him to flee when he is confronted with it. It could be something as simple as the fact that his nose is too big, or that he is a small and nebbishly wizard pretending to be some vast, powerful demonic power. When his shame is revealed, he is too humiliated to continue; this is a good option for comedy adventures.
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 QuandrySaving Quandry
Finally, another classic quandry puts the heroes in the position of choosing between a grand opportunity to hurt the Master Villain -- or saving the lives of a number of individuals.
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.