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.
GoalSettle a Debt
A player character may find himself in the position of needing to settle a debt. He could gamble away all his money and need to raise some more to repay the gambling house before its enforcers come for him. On a more personal level, the character may need to settle a debt of either money or honor that he owes to an NPC.
Story HookPressing Buttons
As a general story-hook approach, think about the player-character -- his personal goals and his personal dislikes. If the hero is pursuing a specific goal, you have one of the minor villains, as a side-effect of the villain's master plan, thwart the hero's latest step towards that goal. Alternatively, if there's something the hero truly hates to see, have it happen -- and have the villains be responsible.
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 SettingOn the Sea
Most of the action occurs on the sea -- the heroes are shipborne for some reason, docking in lots of ports. Again, this is good for adventures where the heroes are investigating clues left all over the map, are part of some trading enterprise, or are being pursued by villains.
Specific Setting ITemple/Church
This can be either the church of some lofty and good diety, or the dark and grisly temple of some horrid deity (doubtless filled with evil soldiers and monsters), or even the temple that the madman villain has dedicated to himself for when he becomes a god.
Specific Setting IIMadman'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.
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 IChief Assassin
The Chief Assassin is the favorite killer of the Master Villain. The Assassin works mostly in the field, first killing witnesses who might prove harmful to his master, then zeroing in on the player-characters. He usually meets his end before the adventure's climax, but he may taken one of the heroes down with him.
Minor Villain IIChief Assassin
The Chief Assassin is the favorite killer of the Master Villain. The Assassin works mostly in the field, first killing witnesses who might prove harmful to his master, then zeroing in on the player-characters. He usually meets his end before the adventure's climax, but he may taken one of the heroes down with him.
Ally/NeutralIngenue in Distress
The heroes must protect some defenseless young innocent who is in danger from the villains. This person, perhaps the sheltered son or daughter of a nobleman or merchant, has no abilities at all but is sweet, charming, and in great need of 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 EncounterBandit Gang
When the heroes are en route from one place to another, have them run across one of the local bandit gangs. The bandits are faster and far more numerous than the heroes. But the bandits stay back. Basically, they're bandits who admire courage and prowess, and the bandit leader will challenge one or all of the heroes to a test of bravery or ability -- such as a horserace, a duel, a wrestling match, a joust, an arm-wrestling match where scorpions sting the loser, etc.
DeathtrapTomb Deathtraps
Another classic type of trap is the sort of triggered trap left behind in abandoned tombs, ruins, and catacombs. Here, a hero who touches the wrong step, floor tile, wall brick, torch bracket, mounted gemstone, or other device will trigger some sort of ancient trap designed to kill tomb-robbers and intruders.
ChaseHorseback
This is a relatively short chase -- it only needs to go on for a mile or so before even the best horses are winded. If it goes on longer than that, the horses may collapse and perhaps die.
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 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.