I can recommend Plus One in San Diego:
Plus One Flyers
Most of their aircraft are at Montgomery Field (KMYF), but some are at Gillespie (KSEE) and Ramona (KRNM). They have a good selection of C172s, including with G1000.
I'm not familiar with northern California, but am going there later this year, so am also interested in reports on rentals in the San Francisco area.