Not really sure how this 16+ year old thread eluded me all this time, but I can add my campaigns to the list.
Order vs. Chaos
500 years ago, the last king of the land decided that he'd had enough with demihumans - orcs, goblins, kobolds, et al. With fervent public support, he raised a vast army of paladins and clerics and eradicated them. Along the way, he tried to enlist every tool of order at his disposal - attempting to gather the pieces of the ultimate "Rod of Law" along the way (the Rod of Seven Parts). Unfortunately for the king, he had some powerful detractors who realized that all that he was actually doing was just enacting genocide on races of people who didn't deserve it. They decided to kidnap his daughter, the Princess in order to convince him to stop his foolish campaign. The king retaliated against these nobles, and had them killed. Unfortunately, they were the only ones who knew where the daughter was (frozen in temporal stasis, and stuffed in a bag of holding). Because she existed outside of time and place. no magic could find her. The King and Queen spent the remainder of their years trying to find her to no avail, and each in their own ways.
Today, along come the PCs, investigating some ancient ruins - shrines that once honored those who fought in these long ago conflicts, where they eventually discover the first piece of the Rod of Seven Parts. Along the way, they eventually learn that the Queen became the Queen of the Hags, and rules over the entire forest, driven mad by the loss of her daughter, and paying a price for pacts she made with evil fey forces long ago. The King became a vampire, and now is driven by evil and hunger, and lurks in the shadows in a land far away. The PCs are driven to complete the rod, but along the way come to realize that ultimate order is no better than ultimate chaos. Also, they discover the actual princess, secreted away in a dark cave, who only complicates the history of the world, and helps them to see that the King's past is not as rosy as the books say.
(in a nutshell: This is Tombs of Abysthor (heavily modified) alongside a (heavily modified) Rod of Seven Parts, with a LOT of history sprinkled in for good measure)
The Best Intentions
An ancient Mind Flayer decides that science progresses far too slowly. In an effort to help mankind along the march of science, he reasons that the real problem is something called "ethics". In an act of infinite benevolence, the Mind Flayer replaces all the most esteemed scientists in the world with Intellect Devourers, and tells them to continue their science "unabated". As expected - all hell breaks loose. Now, all the world's most prominent alchemists are free to test their creations on an unwilling populace. The need for "test subjects" grows exponentially as the alchemists have free reign to hasten their testing. One alchemist even creates an "alchemical plague" and unleashes it on a very large populace. The plague isn't healed by traditional magic, and lowers strength by 1 point per day, until they go into a coma. At this point, priests, disguised as Priests of Kelemvor, offer to "remove" the "dead" from the city, where they are promptly cured with an antidote, and thrown into slavery in a far-off land over the sea. Here, they are given over as test subjects in brutal, and often bizarre experiments.
Also, the Mind Flayer has learned that one of the scientists has been experimenting with the Apparatus (from Ravenloft, and the Book of Artifacts) - a sinister device that can transfer the intellect of one creature into the physical body of the other. He's decided that he wants to recreate a much larger version of this device around a Tarrasque that he's found trapped in an earthen prison near a jungle. If he manages to pull this off, the party will have to deal with a Tarrasque with the intellect of a mind flayer!