A few cautions: The drive to the lake from hwy 120 on Cherry Oil road is rigorous. Allow an hour for the ~23 miles and make sure that your vehicle is not prone to overheating on very steep hills. The lake can be quite windy, setting up some pretty choppy water, especially near the damn.
My husband and I have rented from a number of places near SF, we make our decisions based on where we want to paddle. California Canoe and Kayak for the Oakland Estuary (510) 893-2617; Sea Trek in Sausalito for Richardson's Bay (415) 488-1000; and Cal Adventures (510) 642-4000. Of course all require experience and potentially a description of how to do a rescue. You have more choice of boats at the first two, but Cal Adventures can be the least expensive if you buy a 3 month pass (unlimited use for $80). Wilderness Sports on Gilman in Berkeley also rent but they are not on the water.