Bukkit

Unite with players and level up.

DiceEaster

Changing gamemode through signs

In Time Based Per world Economy Plugin(other economies can be run)

A simple way to give spawners

Fully customize weapons, armor and tools with custom RPG stats with custom damage types, custom defense types, 25 item stats, and tons more options.

WGamemode - Gamemode in WorldGuard Regions!

ButtonsPlus allows you to assign various commands and actions to buttons without the need to type any commands!

TabGroup

A plugin form of SethBling's DeathSwap!

A fully-customizable plugin to create CS:GO like chests in MineCraft

Easy parkour plugin for Bukkit

SaveItems

Create snow in the defined area.

RainAway allows rain / thunder cycles to be skipped

HG Soup

Making sponge useful again, now with lava too!

LotsOfCommands is a bukkit-plugin in progress that supplies a server with a variety of useful and fun commands.

Transport-Pipes as plugin (like Buildcraft)

Send and recieve friend requests, stopping combat between friends.