Bukkit

Cool multihome plugin.

Enderdragons+

A standalone IRC server plugin for Bukkit with ingame chat, where ingame users show up as separate users on IRC.

Steel Security

Inception is a plugin to allow world overlapping

Makes creating a Prison server even easier!

Complete RPG Mod, featuring Races, Classes and skills.

Convert worlds into instanced dungeons.

Individual Signs Plus

Elevate Your Fishing Experience in Minecraft!

You'll never have to worry about getting bacon again...

Adds loads of new firework related features!

Utilize the features in Spout using SpoutEssentials, for a whole ton of fun!

SmartServerTool

LuckyBlocks

From the Reddit thread for Miner Apocalypse, prepare to be utterly alone.

Limit Pointless Mob Spawns + Reduce Lag!

Optimize your server by reducing entity lag, cleaning up the world and more!

A TinkersConstruct-inspired Plugin; Replaces Vanilla-Enchantments

Easy prefixes and suffixes for in-game chat using permissions (Simple Prefix)