Random Adventure Generator

ThemeRomance
This sort of adventure (rarely played, but worthwhile anyway) has as its central plot the romance between two characters, usually a player-character and an NPC.
GoalEscape
Early in the adventure, the heroes are captured. The remainder of the adventure consists of them learning enough so that they can escape. They have to get to know their fellow prisoners, learn the prison's routine, inventory their possessions, acquire other possessions they need, plan an escape, and execute it.
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.
PlotGeographic Progression
This is the simplest sort of adventure plot. The heroes have an area to investigate or travel through; they have encounters based on where they are. For instance, the traditional dungeon, where monsters are tied to specific rooms or areas. Or, if the heroes are travelling along a narrow valley or through an enchanted forest, they might suffer ambushes and other encounters fixed to various points along their travel plan. The plot, then, is getting to the villain by surviving the intervening obstacle encounters.
ClimaxChase to Ground
First, you have the Heroes Chasing the Villain. The villain, after a series of encounters with the heroes, is running to safety, to some place where he can acquire more power, or to somehwere he can accomplish some dread purpose such as assassination or mass murder. The heroes chase him, have to deal with the obstacles he leaves behind, and finally catch up to him before or just as he reaches his goal. Here, we have the final duel between the villains forces and the heroes. Second, you have the Villain Chasing the Heroes. Often, in a story like this, the heroes have found out how to defeat the villain -- such as getting to a particular temple and conducting a particular ritual. The villain chases them all through their quest, catching up to them just as they're commenciing their ritual; they must, with heroic effort, conclude the ritual while suffering his attacks. Third, you have the Master Villain's Sudden Escape Attempt. This takes place in adventures where the Master Villain's identity is unknown until the end. His identity is revealed and he makes a sudden bolt for freedom; the heroes give chase. This usually results in a dangerous foot-chase through nasty terrain -- such as across rooftops, through the dungeons, or across an active battlefield.
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 IDemi-human Community
In wilderness areas, this will be a large community of demi-humans -- elves, dwarves, halflings, whatever -- or intelligent nonhumans such as orcs. If your action is taking place in a city, this could be a hidden community (such as a secret underground dwarf community) or a section of the city inhabited mostly by demi-humans.
Specific Setting IIPalace of the King
The heroes could be here for many, many different reasons: Trying to get a favor from the ruler, part of some nobleman's retinue, members of the palace guard, sneaking in to save the ruler from assassins, sneaking in to assassinate the ruler, thrown into the dungeon for crimes they did or didn't commit, etc.
Master VillainCorruptor
The Corruptor is the villain who wants to make something nasty out of something that is currently nice. He may be working on a small scale -- i.e., wish to corrupt one character or a few characters, particularly PCs and their favorite NPCs. Alternatively, he may be a big-scale villain trying to change an entire city or nation into a jaded, debased pit of sin, hatred and death.
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 IIHard-Eyed Advisor
This is the sort of villain whom the heroes see in the Master Villain's throne room. He's hard-eyed and scary; life means nothing to him and he enjoys killing. He's also a good advisor to his master.
Ally/NeutralVillain Ally
For some reason, the heroes find themselves in the company of a villain. Perhaps he's a minion of this adventure's master villain; he may be guiding the heroes to wherever they must leave a ransom, or, if the master villain is forcing the heroes to perform some mission, this villain ally is along to make sure they do it right. Whatever the reason, he's competent, unpredictable, and out for himself.
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.
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.
ChaseEndurance
The Endurance Chase is not some sort of climactic chase -- it's a rugged, tiring, persistent pursuit that tests the characters to their limits. In this chase, the heroes and villains are pursuing one another across a lot of territory and they're not catching up with one another very fast. This may be a horseback pursuit across a hundred miles of savannah, a camel chase across several days' worth of desert, or a chase across arctic tundra.
Omen/ProphesyInnocent Fulfills Prophecy
An innocent could fulfill a prophecy -- one which endangers his/her life. This innocent might, for instance, be the one who is supposed to slay the king, but is not a mighty adventurer able to protect himself from the king; the heroes may find themselves sheltering and helping this poor dupe.
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 ConditionNo Hurting the Villain
For some reason, the heroes cannot afford to fight the villain directly. For instance, what if a demon possesses the body of the child of one of the characters, or a very important child spoken of in prophecy, one without whom the world will perish?
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 HerringLying Rumor
This is the worst and most useful type of red herring -- the interesting rumor which just happens to be false. In adventures of this sort, the best Lying Rumor concerns the Master Villain; it gives the heroes some "important" information about him which later turns out to be useless.
Cruel TrickNPC Turns Traitor
He may alert he enemy when the heroes are planning a raid; he may steal the artifact and take it to the villain; he may stab a hero or important NPC in the back (literally) before departing.

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