Bukkit

MobArena

Survive hordes of zombies as night stretches forever on

Modular Minecraft server plugin - put no unnecessary strain on your server. Build just what you need.

Custom enchants from books, like CosmicPVP!

Drive in Minecraft

PwnFilter - The return of your favorite RegEx Chat Plugin, block swears, fix .command & more!

A simple plugin to protect villagers and related mobs

Auction off your items

A custom enchantment plugin based on Zenchantments

Adds loads of new firework related features!

Jobs

MagicCarpet - Take yourself wonder by wonder

Automatically sends mined blocks to a player's inveontory

Adds magical runes to the game for Teleportation, Construction, and Combat

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

A simple lightweight clan plugin.

Universal

LuckyBlocks

Add survival-friendly craftable mini blocks to Minecraft!

A complete match and event framework for creating arenas and minigames in Minecraft. Supports creating modes through config files, or fully custom modes through plugins.