Bukkit

PingReply

Sync your players experience over many servers using MySQL.

StingerMissile

NoFarm - No more mob farms; Mobs drop items only when killed by player

A GriefPrevention Addon that allows selling / buying claims using signs.

It is a Parkour plugin which let's you create and Play Parkours

InventoryPlus

Destroy a glowstone with a pickaxe and get a block back

Replaces conventional chat-based mailing systems with books and physical mailboxes

Format CraftBukkit console log entries

uPlanes - Planes in Minecraft!

Skyblock Co-Op

Easily create queues for attractions and areas.

Create competitive hunts for rewards and prizes.

DroxPerms

Dynmap-SimpleClans

#1 Scoreboards plugin!

Easily get the price of all the items by just setting the price of 'raw' items.

Create massive trees in Minecraft! Choose your own sizes and block types!

Allows admins to keep notes on players.