XNA Camera Direction from Orientation

_cameraDirection = new Vector3((float)Math.Sin(_cameraAngle.Y) * (float)Math.Cos(_cameraAngle.X),
       -(float)Math.Sin(_cameraAngle.X),
        (float)Math.Cos(_cameraAngle.Y) * (float)Math.Cos(_cameraAngle.X));

Forward vector from euler angles:

public Vector3 _Forward
{
 get
 {
  return new Vector3((float)Math.Sin(_orientation.Y) * (float)Math.Cos(_orientation.X),
        -(float)Math.Sin(_orientation.X),
         (float)Math.Cos(_orientation.Y) * (float)Math.Cos(_orientation.X));
 }
}