After having the water main turned off and back on, there is no cold water to my shower. Obviously, with everything else working fine, there is something clogging that line. How might I free it up?

Opening and closing the main may have dislodged some debris. Shut down the main and remove the shower valve stem or cartridge. Turn the main on briefly while you hold a towel over the shower valve. Inspect and clean the valve and then reinstall. You should be good to go.