I just recently sold a car here in CA. After reading so much about all the scams from Craig’s list, etc., I was very paranoid regarding personal checks/money orders/cashier’s checks. Fortunately, the buyer was cool with cash (and the amount was $4100, so it wasn’t too onerous to carry that amount in $100 bills).
On your title, there is an area that you will need to fill out an have both buyer and seller sign; this gets mailed to the DMV to attest to the fact that as of the date of the sale the seller no longer has responsibility if the car is in an accident.
You will also want to print out a bill of sale from the CA DMV here. This needs to be filled out as well.
I don’t recall if there is anything else that needs to be done, but browsing around the DMV’s site should answer any proceedural questions you might have.