This is a cool side trek that my Hand of Light group finished running a few weeks ago. To the right are links to PDFs of the adventure and the maps to accompany it.
The campaign is set in Waterdeep, and the heroes had offended the Guild of Apothecaries and Physicians, one of the most wealthy and powerful guilds in the city. The guild (known as the GAP) had been making their lives generally unpleseant, but recently the GAP may have (or may not -- not even the players really know) arranged for some of the heroes' gnome alchemists to be arrested for selling illicit drugs. The group has some gnomes making healing potions for them and also selling them in the market for a profit...but that's a different story.
Anyway, the GAP basically makes a deal with the heroes. If they retrieve this magical Amulet of Mraphadyr, the GAP will use its political connections to have the gnomes released.
The heroes go through the whole adventurer, get the amulet, and then decide NOT to give it to the guild. (This is the sort of twist that as a DM I love, because it just gives me more complications and trouble to throw at my poor players. Yar!)
Overview: The heroes are tasked with retrieving a magical amulet from its last known location, a swamp, in order to make peace with a powerful organization they have offended.
Creatures Encountered: plesiosaurus, lizardfolk, kobolds (yay!), trolls, "acidic" earth elemental, and a young black dragon.
Levels: This adventure is designed for a party of 5 characters, levels 8 through 11.