Limit online players by rank and allow them to queue
ActivityTracker can log new player activity into a single log file
Heimdall anti-grief: automatically detect and ban griefers
Simple Lift Signs for Bukkit
HomeSpawnPlus gives you control over spawn/home behaviors
honeypot griefer traps
Log ores being mined to look for cheaters.
AfkBooter - Boot players who idle too much on your server
Record "/who" results in your server.log file
