Bukkit

Minebook is a chat related plugin that modifies the join/leave messages for specific players.

For example, if I wanted to use it on my server, it could be used as following: The glorious lord "username here", has enlightened us with their grace here in "world name here." We could also change the colors of this in such that my name is red and everything else is yellow.

We could also apply this to groups of people such as the default group: The newly spawned "enter username here" has just inhabited "enter world name here."

In addition, this plugin can also customize the leave message.

Such as: "username here" is no more in "world name here"

All in all, this plugin offers the customization of leave and join messages for groups or specific players. How you incorporate them is up to you.