I am doing finite volume Navier-Stokes Computations for external flows in 2D, both cell-centered and cell-vertex based methods. I would like to get some information regarding the implementation of wall boundary conditions, and some references on the same. Thanks in advance.

You can implement convective flux terms and viscous terms separatly. For the convective terms, all you need on the wall is the pressure, and the mass/heat flux terms are zero everywhere on the wall (except for heat transfer calculations using non-adiabatic wall, in that case, the heat flux is not zero). In the viscous terms, the velocity on the wall is zero.

For cell-vortex based method, the control points are on the wall itself, so the pressure and velocity conditions can be dirctly applied. For cell-center based method, the pressure on the wall needs to be extrapolated from the interior control points. You may read the following artical to get useful hint: Rizzi, A. "Numerical Implementation of solid-body boundary conditions for the Euler equations." ZAMM, Vol. 58, pp. 301-304. (1978).