California's rulings are the most followed by other states, according to this wikipedia entry.:
Reputation
As the Wall Street Journal explained in 1972:
"The state's high court over the past 20 years has won a reputation as perhaps the most innovative of the state judiciaries, setting precedents in areas of criminal justice, civil liberties, racial integration, and consumer protection that heavily influence other states and the federal bench.”
Statistical analyses conducted by LexisNexis personnel at the Court's request indicate that the decisions of the Supreme Court of California are by far the most followed of any state supreme court in the United States.<7> Between 1940 and 2005, 1,260 decisions of the Court were expressly followed by out-of-state courts (meaning that those courts expressly found the Court's reasoning persuasive and applied it to the cases before them).
http://en.wikipedia.org/wiki/California_Supreme_Court#Reputation