Random Adventure Generator

ThemeAction/Adventure
This is the most common and straightforward sort of adventure there is. In the Action/Adventure scenario, you present your characters with a task and then confront them with obstacles to overcome in order to accomplish the task successfully.
GoalRescue NPC(s)
The characters must rescue one or more kidnapped NPCs, probably from the stronghold of the kidnapper. Obviously, they must get to said stronghold, break in, rescue the kidnappee, break out, and escape back to safety; this usually requires careful and clever planning and a large dose of luck.
Story HookMystery Woman
Create an NPC "mystery woman" sure to be fascinating to your hero and have her keep appearing inexplicably in his life. As he becomes interested and investigates her, he keeps stumbling across the villain's plans and becomes inextricably mired in the plot. (For female player-characters, the Mystery Man is just as useful.)
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.
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 ICraftsman's Quarter
This can occur in either the shop of the master craftsman of a palace or manor, or the guild-area of a city.
Specific Setting IITavern/Inn
This is a classic fantasy setting, the residence of travelling heroes and the home of the tavern brawl.
Master VillainDestroyer
This villain is like the Corruptor, except that he likes destroying instead of corrupting. He operates like the Conqueror, moving in his armies -- often nonhuman or monstrous armies -- and destroying everything in sight. Again, the Destroyer could easily be an evil god or demon, meaning the heroes wil have to find his weakness in order to thwart his current plan.
Minor Villain ISnivelling Vizier
The Vizier is a throne-room villain. Functionally, he's rather like the Hard-Eyed Advisor, offering tactics and advice to his master; but he's an ooily, sleazy, cowardly sycophant. He's usually brilliant in his field of advice but has no combat abilities.
Minor Villain IICorrupted Hero
This villain was once a hero, possibly one known to the players. He was seduced by the dark side of the dungeon master. Because of his own weakness, or of a curse, he has become a villain, a pawn of the Master Villain.
Ally/NeutralGrumpy Old Professional
Again, the heroes need an expert in a certain field -- this time a craft or art, such as blacksmithing, engineering, horse-training, or whatever. The only or best professional they can find is an aged expert. He's grumpy, cranky, and sharp-tongued; he constantly complains about the food, the weather, his companions, the decline in skill of his co-workers since he was a young man, the road conditions, the rotten pay he's receiving, and so on.
Monster EncounterRavager
This is another classic monster encounter; the monster which is bedeviling a community or local area and will continue to do so unless the heroes destroy or defeat it. Yes, this is similar to the Master Villain of the same name, but the Ravager usually has no master plan -- it just wants to kill, destroy, or eat.
Character EncounterInquisitive Official
Some local authority has noticed the characters' presence and it makes her curious. She snoops around asking questions all the time. She may be a city guardsman or special agent of the ruler, but (functionally) she's a police lieutenant, asking the rong questions at the wrong time; the heroes have to work around her, sneaking where normally they'd be able to work in the open.
DeathtrapStampede
Should the heroes ever cross plains or prairies, their villainous enemies may wish to stampede a herd of large animals at them. Alternatively, beasts in the forest may be stampeded by fires set by the villains; in this case, it will not be one sort of animal charging through, but a mixture of terrified forest animals, from the smallest fox-cub to the largest bear.
ChaseFootrace
The chase involves the characters on foot, probably through such terrain as city streets or the corridors of a palace. One hero may realize that the's being pursued by a party of enemies and choose to run for it; the heroes may have caught up to the Master Villain, prompting him to run for his life.
Omen/ProphesyComet's Progress
Events during the adventure may be enlivened by a large and menacing comet which appears in the night sky for several days during the scenario; the locals take it for an omen of doom. The comet may be the result of magic being used by the Master Villain, or the comet's appearance can pertain to an old legend involving the Master Villain.
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 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 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 TrickVillain Accompanies Party
In this distressing situation, the Master Villain, in disguise or his secret identity, accompanies the heroes for much of their quest. He gets to know them, learns their strengths and weaknesses, learns their plans, and just as soon as it's most efficient for him, he thwarts their current plans and leaves. Alternatively, the Master Villain might be with the heroes all along, up to the very end; the heroes know that one of their companions is the villain, and the whole thrust of the story is finding out who he is. This is the whole purpose of most Mystery-type adventures.

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