Bukkit

Tame those Endermen!

User registration and nickname protection with OpenID

PailStone extends the capacity of users to interact with redstone and vice versa.

RolePlayMobs - WARNING Its just an Idea

Prevents dragons from spawning

A Quick Way Of Notifying Users When They Can Vote Again

Counter Craft

Customizable Colored Op Usernames, and More!

A new way to power block with signs.

BlockNotifier

Global banning system

Channels based, configurable, permissions respecting chat plugin.

Valve

City simulator

Provides basic functions to inform your players if the server is under maintenance.

Casino

A simple mob spawner plugin

Spectre

Curfew

This plugin allows players to create "private warps". Players also have various other tools and admins have full control.