The publication of the book written by Skeeter and Aibileen is the most important event in the novel. This event is arguably the most important of the novel as it leads to the climaxes of each of the narrators' stories (Skeeter, Aibileen, and Minny). The values and efforts of these characters are manifested in this event.
The Benefit is another highly important episode. Here the conflict between Celia and Hilly comes to its climax (and soon after comes to its conclusion). In terms of the plot progression of the novel, the Benefit is central to the story as it has been foreshadowed heavily and serves to organize the action of the novel to a significant degree.
Other imporant events are Celia's miscarriage, Skeeter's showdown with Hilly, the cancer diagnosis of Skeeter's mother, Mae Mobley's first lesson on the toilet, and the end of Skeeter's relationship with Stuart.