Bukkit

Vault is a Economy/Permission plugin for hooking into the various Economy and Permission plugins.

WorldGuard

A collection of useful commands and features for server admins and players.

Plugin Manager For Bukkit

EssentialsX

SetSpawn

Allows server admins to easily modify how Minecraft works without programming anything

Change your ingame skin

A plugin which teleports you to your set home.

Tablist

Fully customize any mobs (and create custom mobs) with a powerful scripting skill system, attributes, equipment, special AI, and much more, along with custom spawners and spawning rules. The ultimate plugin for making RPG servers and minigames.

mcMMO

Change the colour of the server chat!

BukkitGUI - the most downloaded GUI for bukkit and any other server

Bssentials GroupManager

An mcMMO themed plugin for horse role-playing.

ServerSigns - Bind player and server commands to signs [1337]

Light weight and easy to use!

An addon to the popular addon Skript that exposes the Bukkit API to general server owners

Unique and challenging custom achievements or quest-like objectives on your server! Books, fancy GUI, rankings, rewards, effects and more!