Bukkit

Guarantees players available space, resouces, and active neighbors, even on a high-population server.

Automatic inventory management for all your players! Defeat the tedium of manual organization! AutomaticInventory

Grief Prevention

Extra Hard Mode

Create custom items and recipes, complete with an API!

[THE ONE TRUE WILD TP] Teleports to random location with no sounds cost and cooldown along with GUI

A pretty simple shop plugin. No signs required. Supports DoubleChests and claim protections!

Bring the concept of regenerating shield "health" from FPS games to Minecraft!

Spectate your killer briefly before respawning, similarily to most FPS games

GriefPrevention addon that provides classification for claims, such as sorting, naming, and a couple other extras

Applies gravity to log blocks (only in trees!) when a player chops ANY tree type.

Actually remove vanilla recipes

Simple, IRC-like chatrooms

GriefPrevention addon: Changes /buyclaimblocks to buy accrued blocks instead of bonus claim blocks.

Vanilla chat that's compatible with administrative vanish/phantom plugins

Teleport between worlds/dimensions without MultiVerse or Essentials

Extend GriefPrevention's softmute feature to vanilla's /me and /tell commands