We apply general variational techniques to the problem of the counterion
distribution around highly charged objects where strong condensation of
counterions takes place. Within a field-theoretic formulation using a
fluctuating electrostatic potential, the concept of surface-charge
renormalization is recovered within a simple one-parameter variational
procedure. As a test, we reproduce the Poisson-Boltzmann surface potential for
a single charge planar surface both in the weak-charge and strong-charge
regime. We then apply our techniques to non-planar geometries where closed-form
solutions of the non-linear Poisson-Boltzmann equation are not available. In
the cylindrical case, the Manning charge renormalization result is obtained in
the limit of vanishing salt concentration. However, for intermediate salt
concentrations a slow crossover to the non-charge-renormalized regime (at high
salt) is found with a quasi-power-law behavior which helps to understand
conflicting experimental and theoretical results for the electrostatic
persistence length of polyelectrolytes. In the spherical geometry charge
renormalization is only found at intermediate salt concentrations
