If you're looking to improve your skills or just want a great day on the water, try Mike Krnaich's Riverrat Wakeboarding School.
A few friends and myself took a lesson yesterday at Lake Sonoma. Mike is a great instructor who can definitely bring your skills up a few levels. Casey Parlette provided excellent driving and he and Mike each took a few runs to show us how to really ride.
I highly recommend his school; get more information about places and costs at http://www.riverratwakeboarding.com