  The Canadian Galactic Plane Survey has opened new vistas on the Milky Way,
including cold hydrogen clouds that bridge a critical gap between the classical
diffuse interstellar medium and the gravitationally bound molecular clouds that
can form stars. The CGPS and its fellow IGPS surveys revealed these
transitional clouds to be surprisingly widespread as HI self-absorption (HISA)
shadows against the Galactic HI emission background. The richness of the IGPS
data allows detailed examination of HISA cloud spatial structure, gas
properties, Galactic distribution, and correspondence with molecular gas, all
of which can constrain models of cold HI clouds in the evolving interstellar
medium. Augmenting the landmark IGPS effort are new and upcoming surveys with
the Arecibo 305m and Australian SKA Pathfinder telescopes.
