Here's a little bit about my campaign: I call it THE QUEST FOR THE MAGNUS LEXROTA.
The characters get word that an ancient evil is about to come back out into the world after being asleep for about 500 years. At the same time, they stumble into an old mage lair and find a triangular piece of decorated gold with a curved bottom. It turns out to be part of an ancient holy relic called the Magnus Lexrota or Great Wheel of Law. There are seven other pieces the characters have to find to put it all together. Since this ancient evil being possesses the Talisman of Chaos, they must put it together in order to even combat him.
The seven other pieces are really just a thread that you can use to string together a series of otherwise unrelated dungeons and adventures. But at the same time, you can throw in some intrigue from other groups who want the Magnus Lexrota for their own, and will do anything to get it.
In my world, the Holy Imperial Church of Hyperion wants the MLR to validate itself. Many of the great Orders of Paladins want the MLR to launch a crusade against its enemies. Minions of the Great Evil want it so their master can take over the world. The gods of Mondalith want the MLR back so they can restore order to the world.
You get the picture. It's really an easy way to use existing dungeons and adventures without going to much trouble. All you need to do is plug in extra-curricular interplay....
Hope that's some help!