Camera spin
In addition to what Martin said about keyframing a 180-degree roll, you can
also try linking everything in your scene to a dummy rotating the dummy
90-degrees on frame 0. This will likely shift the entire animation to an
orientation in which you won't ever being passing the camera over the
singularity at the poles. Note that the singularity is just an artifact of
quanternion mathematics, which was originally developed in the 1800's to
inhibit the gimbles on big sailing ships from locking. All high-end 3D
animation systems use this form of math for smooth motion, but like anything
it's not perfect.
– G