Random Adventure Generator

ThemeMystery
Here, the characters are presented with a mystery -- often a murder -- and have to find out who did what to whom.
GoalThwart Monstrous Plan
This is a classic fantasy-adventure plot: The characters learn of some horrible plan made by a monstrous enemy, and must thwart it before the kingdom is lost or the world is destroyed. This is an epic goal, and usually requires that the characters go to all sorts of places, rounding up allies and artifacts, before being strong enough to face their enemy.
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.
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.
ClimaxPrevented Deed
Here, the heroes have been defeated -- captured by the Master Villain, or so thoroughly cut up by his minions that all believe them to be dead. And the heroes have learned, from the bragging of the villain, loose talk of his minions, or examination of clues, what is the crucial event of his master plan. In any case, the battered and bruised heroes must race to this site and have their final confrontation with the villain, bursting in on him and his minions just as the knife or final word or key is poised, and prevent the awful deed from taking place -- and, incidentally, defeat the master villain and minions who beat them previously.
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 ILost City
This is the remnant of some lost civilization or expedition, still thriving in some forgotten corner of the world. Remnants of lost civilizations can even inhabit cavern systems beneath campaign cities, preying on the above-worlders for their goods, slaves, and sacrifices.
Specific Setting IIMansion 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.
Master VillainOrganizer
This Master Villain is the head of the local criminal syndicate -- the Thieve's Guild or slaver ring, for instance. He's cold-hearted and unsympathetic, and human life means nothing to him. He employs assassins and musclemen against the heroes, and can only be reasoned with when it's going to profit him more to cooperate with the heroes than kill them.
Minor Villain ICoward
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.
Minor Villain IISnivelling 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.
Ally/NeutralTragic Fellow Hero
The heroes are in the company of some hero well-known to them; he may have been a companion or ally, or they may just know him by reputation. He is a tragic figure; he may have lost his family to the master villain, or lost his properties and titles, or be afflicted with a curse he cannot be rid of, or be committed to a quest he knows will take his life. He's dour, and gloomy, prophesying doom and having no fun at all.
Monster EncounterAssassin Monster
This mosnter, at some time in the adventure, is sent by the Master Villain to attack one or more heroes when they're at their most vulnerable -- asleep, enjoying themselves, etc. Usually, the Assassin Monster attacks, but the hero, though injured, is able to hold it off long enough for his friends to respond to his shouts. The Assassin Monster is usually killed by his friends, who can then speculate on who sent it and why.
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.
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/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 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 QuandryFriend Quandry
At a critical point in the story, one of the campaign's NPCs makes an impossible demand of one of the heroes.
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.