We heard the rumor, but now it's official — Warner Bros. TV has greenlit a Supergirl to be executive produced by Arrow mastermind Greg Berlanti and Ali Adler, who made No Ordinary Family with him. I'd say this make the odds of Supergirl joining Arrow and The Flash on The CW not insignificant.
Of course, right now the show could end up on any channel — Constantine is on NBC, while Gotham is on Fox — but the Berlanti connection suggests WB might continue to keep it in the family. The Hollywood Reporter stresses that it doesn't know whether the show will be 30 minutes or an hour, but that the title will not be Supergirl, I guess because... uh... WB already had enough DC shows with clear titles? Hell, I don't know.