Our group really prefers entire adventure paths (and mega adventures) to just one-offs. We've played in a lot (but finished few). I've read many more. Here are the ones I'm most familiar with:
Red Hand of Doom
Scales of War
Shackled City
Rise of the Runelords
Legacy of Fire
Kingmaker
Skull and Shackles
Revenge of the Giants
City of the Spider Queen
3.5 Eberron series of adventures (Shadows of the Last War, et al)
4e series of adventures (H1 - E3)
Expedition to Castle Ravenloft
4e Tomb of Horrors
3e Tomb of Horrors
War of the Burning Sky
However, I have to say, there is only one adventure path that our group talks about constantly. It's the only one we send e-mails back and forth on a frequent basis and which we post on forums about. When we don't have the time or people for a full session, we go out to dinner just to talk about the campaign and make plans. It has a perfect mix of combat, action, intrigue, mystery, and roleplaying. We've identified with the setting itself more than any other setting I've been a part of. Just last night, the DM and I were recapping our adventure over Vent to a fellow gaming friend who joined the military and moved away several years ago. Not only could I could recall everything we had done in vivid detail, I found myself recalling the name and description of nearly every NPC (including minor ones), as well as the name of every country, planet, and plane, and many even more minor details. Such a connection has never happened for me, even for those games in which I DM and type up copious notes. Our friend was enthralled by our discussion and kept asking for more details. He couldn't believe that we were actually playing in such an intricate, detailed, and frankly awesome campaign.
This AP is none other than EN World's own Zeitgeist. And it's the only campaign that I've ever
known that I'd be finishing all the way to 30 (we've alreay made plans to use Vent and Map Tools in the event the DM has to move before we're finished).
