  Tomographic intensity mapping of the HI using the redshifted 21 cm
observations opens up a new window towards our understanding of cosmological
background evolution and structure formation. This is a key science goal of
several upcoming radio telescopes including the Square Kilometer Array (SKA).
In this article we focus on the post-reionization signal and investigate the of
cross correlating the 21 cm signal with other tracers of the large scale
structure. We consider the cross-correlation of the post-reionization 21 cm
signal with the Lyman-alpha forest, Lyman-break galaxies and late time
anisotropies in the CMBR maps like weak lensing and the Integrated Sachs Wolfe
effect. We study the feasibility of detecting the signal and explore the
possibility of obtaining constraints on cosmological models using it.
