Bukkit

Add more explosives to Minecraft!

Make any recipes through GUI's only - the only plugin that supports itemmeta, like enchantments - The most powerful crafting plugin.

Make statues for your players to enjoy.

Create customized, automated poker/blackjack tables and play with your friends!

A mob catcher where you throw catch capsules at mobs for a chance to catch them.

Dropped Heads from all Mobs and Players!

GWMCrates

An SMP plugin that allows players to bend elements as in the Avatar world!

Adds Working Elevators to Minecraft!

Customize villager trade lists for fun, profit, or a more balanced economy.

Best plugin for death swap!

BukkitSpeak

All an admin needs (/vanish, /invsee, /rank, /troll, /tools (GUI) and many many more)

Ever wanted Hashtags(#) and At Signs(@) in chat? Both metered to see how many times that particular sign has been used!

Double your exp and change it into cash

SpeechBubbles Reloaded

TradeMod is a plugin that allows players to safely trade with each other.

this is a parkour plugin

PetShop let your user buy any Monster you can imagine

1.5.1 compatible SkyGrid mod based off of SethBling's idea.