This Blog post provides the best Zigbee Projects

Wireless sensor network for real time air pollution monitoring using Zigbee

Online monitoring of CO2 Storage and Leakage detection

Forest fire detection based on Zigbee networks and Matlab

Smart Home using Zigbee

Patient monitoring system using Zigbee

Machine to Machine communication

Smart irrigation system using Zigbee and Wifi

Zigbee based defence robot

Industrial data acquistion and monitoring using Zigbee