Bukkit

Change the format of the console /say command.

Admin mode & Admin GUI

ControllableMessages

Kick people that used clients like MineChat

ChatUtils adds several functions to the chat, including colors, logging and caps blocking.

Displays real-time tweets in Minecraft chat.

Chat prefix

Allows you to create custom rank tags/server login messages/chat colors!

Monetise your server with Minecraft map images (in-game advertising)

Display different MOTD's for each world!

Chat CleanUp

messagecoloredsheepmcs

Communicate with the outside world via SMS, Facebook, Twitter and more!

The best PvP Stats plugin, simple and easy to use!

Integrate Dynmap web chat with HeroChat v5.5+

Stop those annoying people, while embarrassing them!

Broadcasts a message to to the whole server that he has to go and how long for.

Compact ID List - Item/ID list for your server!

A simple plugin which allows players to create their own Alliance Tag to be shown as a suffix.

Inserts a prefix when the player chats, telling what world they are in