Bukkit

Extra Hard Mode

EntityManager

This allows players with permissons, to give other players points

BlockEnderChest

List all banned players on the server.

Automated taxes and salaries

Emphasize sarcasm.

GroupDrops

Jail++ is a fully-featured Jail plugin for Bukkit, and it's the official successor of Jail, JailLikeHell, and SimpleJail.

WorldChannels

Karmiconomy

Creates effects when players move.

Old-school style lottery plugin

Custom jail plugin based off of imjake9's SimpleJail

Command-based community item sharing with anti-leech karma system

Actor allows you to create NPC actors which playback pre-recorded actions in world.