Bukkit

AntiSwear

FatTnt

Build structures with commands and sockets!

Allows server admins to create their own inventory menus to perform scripted commands in a similar manner to command blocks

Toaster

Instantaneously kill mobs with hand. /instakillmobs (gamemode) (enable/disable)

allows you to see commands being used by other users.

GamemodeDetector

When you're not playing /spec on gets you a teleporter and flight. You're invisible to players alive and you can't do damage.

An entity and memory cleanup utility plugin for Bukkit

AutoRegionGuard

SuperTab

Simply and useful plugin for /vote and VoteListener.

Doors made out of blocks - from the ol'skewl HeyO mod

A Fake Quit/Join plugin

Ban people/subnets/countries from "offline" servers

Create your own Coupons

Simple plugin to prevent interaction with blocks and paintings.

mcMMO and Vault GUI

Skyauth