Bukkit

Custom GUIs

Gadget - Inspect all Bukkit events at run-time

Test your server to see if it is working!

Allows you to say anything from player. (command too)

A powerful permissions system addon for Essentials/PEX/etc

A tool to combine all other tools

you can change everything

A tool that allows URLs to be shorten in-game

A powerful, lightweight Minecraft server management plugin with 40+ commands

CommandAbbreviation

InfinaTime - Constant Time For Your Server

Manage warnings to players in game for those who don't want automatic player reprimands

Bans the most well known hackers and griefers

Use this API to make blocks fall out of the sky

Allow players to join a full server.

MetaCopy allows you to copy and paste an items meta to another item!

Spigot plugin for players localization

Lua for Bukkit.

The Plugin can control your minecraft server remotely from chat

Utilities for Minecraft server version info