Heavenly Horse From the Outermost West - Mary Stanton
Definitely agree about the Ramona books. Do those first, then the Henry Huggins and Beezus books to fill in the background. The older ones are a bit creaky - I read Henry Huggins when I was a kid.
Also agree about the Oz books, not stopping with the first one.
Winnie the Pooh - the real books is great too, as well as Alice in Wonderland.
I read a lot (over 30) of the 1950s - 1960s Nancy Drew books to my daughter. When she got older I read some of the Nancy Drew/Hardy Boys joint books, since they are a bit more advanced (people actually get killed in them.) We also read some of the 1930s reissues, but they are a bit racist in spots.