Marine Stadium is my local spot: its salt water. Nick Heaney uses an older X-star out there. There aren't too many wakeboarders in OC and all the people I've seen nick teach are all beginners. Definitely go during the week. If you go on a weekend, you will have a BAD time. Also, check the Stadiums phone recording for closure dates. 1(562)570-3203.
WakeSports Unlimited Is awesome, all the guys there are down to earth and are pumped to hear about your own stories. They own a shop and a launch ramp in Carlsbad Lagoon so check with them for demo days and such. I thinks its $25 and you get lunch and a set behind a axis A20 and I think a nautique 210. (don't qoute me on that though). The lagoon is about an hour drive from Anaheim on the 5 freeway.