Futaba GY401
From RC Helicopter Wiki
The Futaba GY401 is a good safe choice for a heading hold mode gyro. The 401 requires an extra channel to be used for remote gain control; if your stock transmitter does not offer that option, consider the Futaba GY201, which has the gain set on the gyro itself.
The GY401 supports digital servos and traditional analog servos, and offers a single travel limit control.