Swan Song by Robert McCammon
Lucifer's Hammer by Larry Niven
The Wasteland Saga by Nick Cole

Ive read more but am currently drawing a blank will post more once I remember.

Jerry Ahern's series The Survivalist, from the early 80's on, not too bad if you like a bit of pulp style post apocalypse books.

Well the only Zombie series I have readed is Dead End by P.S Power, I loved it mainly for the characters interactions but you migth enjoy it for the sci-fi element.

Black Tide Rising series by John Ringo is awesome zombie apocalypse stuff
The Last Centurion also by Ringo is a great plague apocalypse novel