Most of mine have been named already: Marguerite Henry and Walter Farley. L. M. Montgomery. Susan Cooper and Lloyd Alexander (Vesper Holly more than Prydain, even if I was a bit beyond the target age when she began). Mary Norton's Borrowers and James Howe's Bunnicula. Edward Eager and Sydney Taylor were massive with me; I've read more copies of Half Magic, Knight's Castle and the All-of-a-Kind Family to pieces than I can remember.

And Betsy, Tacy and Tib. Maud Hart Lovelace. None of the later books with them as teens and adults were in print when I was a kid (though the minute they came back in I pounced on them), but I read the first four over and over. Oh man, I loved Tacy. Tacy and Anne were my sisters in red hair.