Bukkit

WorldGuard

Keep your inventory in a chest when you die !

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

Player and Mob Heads Full-featured plugin

Expand the capabilities of Skript with skRayFall

Mine spawners with silk touch

Mine spawners with silk touch / Spawner Management

Inexpensively protects your ores from cheaters.

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

Simple Sit

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

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

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

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

Herobrine

Orebfuscator - Anti Xray

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

Manage entities on your server

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

CombatLog punishes players who log out to escape combat.