I trained at Helistream at John Wayne (KSNA). Good school -- at least it was about 8 years ago.
http://www.helistream.com
At Chino (KCNO, my home base) you've got Silver State Helicopters. You can't swing a deat cat at Chino without hitting an R22 these days. They're going crazy. Radio ads and everything.
http://www.silverstatehelicopters.com No idea if the flight academy is any good. One nice thing about CNO is that there are a buttload of RVs based there.
Long Beach (KLGB) has a helicopter flight school but I forget what it's called (sorry).
Torrance (KTOA) is home to Robinson Helicopter and has both Pacific Coast Helicopters (
http://www.pacificcoasthelicopters.com) and JJ Helicopters (
http://www.jjheli.com).
Lots of options. I'm sure there are many more in SoCal.