Politics and intrigue between nations or along a frontier, leading to war. Not an AP with "a battle." I want a military campaign with armies on the move, charging horses, battles, clashing armies, feints, retreats, alliances, diplomacy, betrayal, the works.
The Frank Harryhausen tribute AP
Mythic journey covering various cool locales and monsters (the Odyssey meets Sinbad meets Jason and the Argonauts)
AP with the coolest dragon encounters and lairs that you have ever built and that we have ever seen.
Cult or alien/planar invasion that the PCs uncover. They must rally an underground resistance movement to fight the invaders. Think V or a few Star Trek episodes or Kull's serpent kingdom.
Mercantile focused AP. Maybe PCs building a merchant house. The trade/merchant analogy to Kingmaker.
Running a frontier keep or port town and the town that supports it.
Fight (or take over) organized crime in a city. The urban underworld AP.
Please no mega dungeons. There are already too many to buy and/or run. Borrrring. I want better than that.