  We present an automated routine to search for HI self-absorption features
within the Southern Galactic Plane Survey (SGPS). The data were taken with the
Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope and
encompass 3 deg by 105 deg of sky in the Galactic plane. We apply our routine
to this entire region and derive spin temperatures and column densities for 70
of the larger HISA complexes, finding spin temperatures ranging from 6-41 K
with HI number densities of a few cm^-3. These `missing link' clouds fill in
the spin temperature and density gaps between dense molecular clouds and
diffuse atomic clouds. We compare the HI emission with 12CO emission and find
that 60% of detected HI self-absorption is correlated in space and in velocity
with a molecular counterpart. This is potentially due to a molecular/atomic gas
transition. We also compare HI self-absorption with Galactic spiral arms and
discuss the possibility of using it as a spiral arm tracer.
