Bukkit

Automatic Minecart (Boat and Horse)

This plugin provides chat-based social interaction.

This Bukkit Plugin will allow you to make headshots on other people and do more damage!

Beat the system! Give yourself any health you want!

DurabilityNotify reminds the user when their tools have low durability. Great in conjunction with mcMMO!

Full featured protection cuboid plugin with factions.

Witch Potions Cauldron

Citizens extension that brings NPC interaction to a whole new level

custom ranking, server administration, and chat plugin for minecraft servers

"Monster Effects" makes monster attack more realistic.

Plugin to play a Vanilla Roleplay. Survive!

Apply potion effects to yourself and other players!

Let your players hunt epic level bosses and craft powerful items from their remains.

A fun alternative to towny/factions with unique features.

A multi-channel chat-system. Can be used as an open-source, and more light-weight alternative to plugins like Herochat.

Plugin to add administrator commands to Gyul's Economy

Use emeralds to craft tools and armor with random enchantments

Vineyards lets you grow grapes and brew wine!

WhoKilledMe

Use the DragonShouts from Skyrim!