Planes rotating to face the camera, but only along one axis I'm using planes as labels on a map over which the camera makes a path. The problem is that if I simply have flat labels they don't look good when the camera is low (blue dots in the animation). With the track to constraint I can make the labels follow the camera (red dots in animation).  The problem is that the labels on the sides also rotate along their Z axis which I don't want. I want the text to always be horizontal wrt the camera, like the labels do in Google Earth.
Try using the Copy Rotation constraint: