Equality California, among the leaders of the No on 8 effort, announced this afternoon that it plans to pursue a same-sex marriage ballot measure in 2010.

They cited a number of factors, including the prospect that many of the gubernatorial candidates will support the measure and that they won’t have to compete for attention and money from a 2012 presidential election.

Other reaction:

Maggie Gallagher, president of the National Organization for Marriage, the single largest donor to Prop 8: “Marriage is worth protecting because it is the way we teach the next generation: children need mothers and fathers. This victory for Prop 8 is a victory for children, for civil rights, and for the common good.”

Andrew Pugno, general counsel of ProtectMarriage.com: “We commend the California Supreme Court for upholding the right of the people to define marriage in our constitution,” said Pugno. “The Court recognized that the power to amend the constitution ultimately belongs to the people. We are very grateful to the Court for agreeing with the arguments we presented in our briefs and in oral argument last March. For the second time now, the people have decided that marriage is reserved for a man and a woman and the Court has appropriately respected their decision.”

Gov. Arnold Schwarzenegger: “While I believe that one day either the people or courts will recognize gay marriage, as governor of California I will uphold the decision of the California Supreme Court. Regarding the 18,000 marriages that took place prior to Proposition 8’s passage, the court made the right decision in keeping them intact. I also want to encourage all those responding to today’s court decision to do so peacefully and lawfully.”

Greg in Hollywood has reaction from celebrities, including Ellen Degeneres, George Takei and Melissa Etheridge, here.

Ellen: “One day when everyone is treated with full equality, we’ll look back and realize how wrong this was.”