At the start of the film, Oscar works with the "Baum Brothers Circus", which is hosted by Frank & Adam. L. Frank Baum was the original author of the Oz series. In the books, Oscar worked with Bailum & Barney Circus, an obvious spoonerism of Barnum & Bailey, and one of several such spoonerisms in Baum's work.
Early on, Oscar makes mention of his shabby jacket. There is a famous story of how a shabby jacket was purchased at a used clothing store for use in Das zauberhafte Land (1939) movie. It was later discovered (and confirmed) that the jacket was originally made for and owned by L. Frank Baum (the author of The Wizard of Oz).
The Tin Man is the only one of Dorothy's three companions in Das zauberhafte Land (1939) not to be directly referenced in this film. The Tinkers are a loose reference to the Tin Man, written in for this adaptation. A Quadling also says that he can work with iron.
Michelle Williams' character Annie is marrying a man named John Gale. Director Sam Raimi has confirmed that Annie and John are intended to be the parents of Dorothy Gale, the main character in most of the original Oz stories.
After the tornado sequence, just before Oz loses control of the balloon, one of the nearby mountaintops is in the shape of the Wicked Witch on a broom.
Sam Raimi: [Object POV] During the tornado sequence in the hot air balloon, Raimi follows the point-of-view of one of the posts from the picket fence.
Sam Raimi: [familiar actors] Raimi is known to include cameos by friends, family, and favorite actors from his past projects. This film includes Bruce Campbell as a Winkie guard; Ellen Sandweiss, Betsy Baker and Theresa Tilly as Quadlings; Raimi's brother, Ted Raimi, as the man who sees the wire during Oz's Kansas show; and two of Raimi's former teachers - Jim Moll and James Bird - as Emerald City townspeople. In fact, Richard DeManincor is the only lead actor from Raimi's Tanz der Teufel (1981) to not cameo in this film.
Sam Raimi: [car] Confirmed by both Raimi and Bruce Campbell, Raimi's personally owned 1973 Oldsmobile Delta 88 appears in this film, and like it's appearance in Schneller als der Tod (1995) it was stripped down to it's chassis and used as a wagon, although it is unclear which wagon.