If you've recently been looking for a gyro sensor to build an NXT self balancing robot, here's another relatively unknown sensor for your consideration. It's the Microinfinity Cruizcore. Find a video of this sensor in action here.
There are currently three gyroscopic sensors available for the NXT (HiTechnic, Dexter Industries and Microinfinity), each with their own specific advantages. In my experience, they all perform equally well when it comes to balancing an NXT robot with RobotC code.
It should be noted however, that currently only an NXT-G balancing program exists for the HiTechnic sensor. It's possible to do this with the other sensors as well, it's just that those programs haven't been made or published online yet.
As I write this, I realize that a comparison page might be helpful. Coming soon then!