A new product announcement by HiTechnic: 

“The HiTechnic Gyro is a single axis gyroscopic sensor that measures the rate of turn in the plane of the sensor.  Using the HiTechnic Gyro Sensor Block for Mindstorms NXT-G, the program will get a signed value that represents the rotation rate in approximate units of one degree per second. The maximum rotation rate which can be measured is +/- 360 degrees per second.

The sensor is housed in a standard LEGO sensor housing.”

Together with the other products announced earlier this week (IR sensor, IR link and motor and sensor multiplexers), it seems there will be a lot more options for NXT in the near future!