A couple more childhood ones that aren't on the bookshelves any more: Nancy Drew & Trixie Belden.
George was also definitely my favourite of the Famous Five, and while Lotta wasn't the main character in the Mr Galliano's Circus books, she was the most interesting. (As an adult, I'm aware there were lots of other problems with Enid Blyton's writing, but that all went completely over my head as a kid)