To perhaps add a bit to the awesome creative juices flowing in this thread, here is what I'm doing with the ideas that I'm eagerly borrowing from earlier posts.
A wicked sorcerer set in motion a ritual that would elevate him to godhood, and he would rule over everything within 1,000 miles of his keep. The ritual was terrible and evil, and a set of heroes set out to stop him. They advanced into his keep, past his guards and traps, and found him in his casting chamber, and slew him, thinking that they would prevent him from completing his act. In fact, they were merely pawns in his great gambit, for in order to complete the ritual, he had to die. He rose, to survey his domain, and found that he too had been cheated. The ritual did make him powerful, powerful like a god. But he was trapped. The ritual broke off a piece of the world, and sealed it into a dark place beside the Shadowfell. He and all of the people in the piece of the world that he'd broken off were trapped. He was the lord of a dead land, where the dead no longer stayed dead, and intelligent beings no longer gave birth. The heroes who thought to stop him were trapped in this land as well. Rifts from the Shadowfell open from time to time, and the dead pour into this place.
I'm still tweaking some aspects of which direction I want to go.
Are the former heroes the key to the dark sorcerer's destruction? Is he keeping them alive and secreted away, knowing that he cannot die while any of them still live?
Its a loose framework, but it gives me the points of light, a big bad guy, and tons of room good story.