Medium Access Control (MAC) for Wireless Sensor Networks has been a very active research area for the past couple of years. The sensor networks literature presents an alphabet soup of MAC protocols. Koen Langendoen is serving the “MAC Alphabet Soup” for sensor networks. The webpage provides a comprehensive index into various MAC protocols specifically designed for use in Wireless Sensor Networks, where energy consumption, latency, throughput, and fairness have a different trade off than in typical WLAN (802.11) networks. You can help contribute MAC protocols not listed in the soup yet.
For an overview of MAC protocols in sensor networks you can read the book chapter on MAC in the “Embedded Systems Handbook” (2005), here.
For an overview of future research challenges for MAC design in sensor networks you can read the recent ACM SIGCOMM CCR article (April 2006), here.