Darkness on the Edge of Town is a sequel of sorts to Ghost Walk, which was in turn a sequel of sorts to Dark Hollow. But if you want those you will need to be quick because the publisher won't be able to sell them for much longer.
So far my favourite Zombie book would be Patient Zero by Jonathan Maberry, with Autumn The City coming a close second. I'm currently reading Dead Beat by Remy Porter, which is Ok but be warned that it has masses of mistakes in it, practically one on every page.
Also worth a look if you like ultraviolence, are the J F Gonzalez books, Survivor and Fetish, and Brian Keene's Kill Whitey.