Darrell Issa might run.
That said, I think James Hahn might want the Attorney General position when/if Harris leaves. Other statewide offices up in 2018 include:
Lieutenant Governor: D: Todd Gloria, R: Steve Poizner
Secretary of State: D: Alex Padilla(Incumbent), R: Abel Maldonado, Dan Logue
State Controller: D: Betty Yee(Incumbent), R: Tony Strickland, David Evans
Attorney General: D: James Hahn, Carmen Trutanich, Ron Galperin R: Stephen Cooley, Anthony Adams
Treasurer: R: Meg Whitman, Robert Dutton D: José Hernandez, Jay Chen, Laura Richardson
Insurance Commissioner: D: Lee Rogers, Hector De La Torre, Joe Dunn R: Michael Villines, Elizabeth Emken
Kingpoleon, those are some good and interesting speculations. Also, since Harris is running for Senate, she'll leave the polls origin vacant if she wins. Hahn sounds like a likely appointee to replace Harris. Cooley came within 1 point of beating Harris in 2010. While he seems like a strong candidate, he still lost, in 2010, and an open seat. It'll be interesting to see who runs in 2018 for Lt. Gov and AG (the latter will probably have a new Dem incumbent since Harris will probably be Senator), as well as Treasurer and Insurance Comissioner. SOS and Controller will have Dem incumbents who will probably be reelected.