Bukkit

Allows you to set your chat, how you want it!

Playing WordMix on your Minecraft Server!

Create optional tags for your players

Sends every joining player a very customisable message!

Simplistic Auto Messaging

Admin Essentials

Reddit

Force other players or even the console itself to chat or perform commands without traces

Change your MOTD every time the server pings!

Cool in chat taunts, actions, and other fun things! Includes option to make your own!

Comprehensive advertisement blocking for those pesky server advertisers

Gives mobs death messages too.

AutoDetector

ChannelTap (ChannelChat)

Text Proximity Chat

ChunkyVillageChannel (ChannelChat)

nutzChat

A chat-based bot-type plugin that you can talk to and have fun with!

If a player is annoying you can do the command /warn <player> <reason> to give that Player a warning.

An allrounder