Bukkit

WorldGuard

Mine spawners with silk touch

Keep your inventory in a chest when you die !

Remove lag and improve the performance of your server significantly with this tool!

Expand the capabilities of Skript with skRayFall

Player and Mob Heads Full-featured plugin

Mine spawners with silk touch / Spawner Management

A plugin to warn your players when your server will restart!

Inexpensively protects your ores from cheaters.

If you've ever used the VeinMiner mod for minecraft Forge, it has now been recreated for Bukkit, CraftBukkit, and Spigot

Simple Sit

Protect and lock Chests, Furnaces, etc. with a easy to use GUI.

Lop off Player and all Mob Heads with configurable drop rates + pvp-farming nerf, includes detailed commands and permissions

A simple but feature-full nicknames plugin that allows you to set other players' nick names

Detect and fight the exploitation of various flaws/bugs in Minecraft!

Orebfuscator - Anti Xray

Keep your server running while mojang is offline, Supports all server versions!

CombatLog punishes players who log out to escape combat.

Manage entities on your server

Paper plugin to enable sand duping. WorldGuard integration, configurable per-world per-block.