Bukkit

Give's hundreds of different particle combinations for players on your server

PvP mechanic using minecraft original gameplay !

JoinFirework

Gives any mob an invitory in which you can store items

Replenishes hand with same tool/block from inventory that was broken/placed

Changes Environmental Damage Values e.g. Cactus and Fall Damage

More effects for your server like blood and stuff

Spawn mobs at a distance by waving a stick!

dynmap addon for adding landmarks

Throw various grenades (12 types as of v2.2) that detonate after configurable time.

MapReplay

Create bounty signs and reward players when the target is found.

A new version of hunters vs speedrunners

Allows admins to send gifts to players though and easy-to-use interface.

Players get banned when they die! Great for some hardcore SMP action!

SimpleCalc - A calculator for servers!

The ultimate healing/health management utility you would ever need!

Inspired by Enzo Knol!

AutoMsg

PsuedoMe - Make other players chat things!