Dominique defending Howard at the Stoddard Temple Trial, at the cost of her job on the Banner. She knows it was going to happen.
Perhaps the most famous moment in the entire book: It's the midpoint, and after a particularly nasty court case (orchestrated by Toohey), Roark's career has been tarnished for what looks to be a really long time. Roark shows up one night at what was this close to being his architectural masterpiece, to look at what it's become. Toohey shows up, and tries his best to get some kind of reaction. Roark just makes like The Stoic. Finally, it's Toohey that loses his cool, and:
Toohey: Mr. Roark, we're alone, here. Why don't you tell me what you think of me? In any words you wish. No one will hear us.
Also after the Stoddard Temple trial, Howard has learned from his mistakes earlier, how to survive during slumps. He's saved money while doing odd remodeling jobs, to pay for his office and for Steven Mallory's rent.
Roark's Badass Boast early on: when someone asks him who's going to let him see his designs through, he says, "That's not the question. The question is: Who's going to stop me?"
Dominique keeping Gail's telegram — "FIRE THE BITCH"— that ended her career on the Banner, as she starts their Masochism Tango. A very graceful case of Forgiven, but Not Forgotten, ironic in a novel where forgiveness is seen as a sin. She only throws it away when Gail admits that he loves Dominique too much for her to hurt him.
Also during their Masochism Tango she makes sure that he gets Hoist by His Own Petard often. For starters when Sally Brent, a fluff columnist, manages to enter the penthouse, Dominique happily gives her the story he wants while Gail wants his wife out of the Papers. She laughs when Gail comes home after firing Sally and tosses the proof cut at her. Another is when she makes him attend No Skin Off Your Nose, a Stylistic Suck play that the Banner had applauded. Gail at first says Anything but That! and was hoping for a quiet night in, but eventually he goes along with it. He does tell her to be quiet about it when she starts saying that the play ought to be in his private gallery.
Monadrock Valley. Monadrock. VALLEY. Howard is chosen to do a summer resort for middle income by Corrupt Corporate Executive Bradley, and he does it by creating it for people that "prefer their own company," giving people their private cottages and swimming pools. What about this Valley is awesome? Several things:
The whole arrangement was a scam, intending for the resort to fail. Instead, the houses become a year in advance, with the exact sort of people that Bradley referred to. As an added bonus, Bradley and his men get arrested for fraud, Bradley's only statement "in apology to his partners" that "I chose the worst fool I could find".
Steven Mallory's righteous fury when he hears of the scam. He may have Jade-Colored Glasses, but he has a point when he points out that Monadrock Valley— Roark's greatest work— was born from someone thinking Howard was a fool.
The buildings themselves are constructed like a musical symphony, as a visiting college student sees. Said student immediately gains "the courage to face a lifetime" and do what he wants to do— compose music.
After this, Roark has no more dry spells during the book. After ten years of refusals, quarries, scandals and trials, he finally has solid standing.
When Gail Wynand hires Roark to build a private home, he attempts his trademark Break the Badass: force Roark into a Deal with the Devil, so that Roark only builds the one house for Wynand and then does cheap commercial enterprises based on classic architecture. How does Howard respond? By giving him what he wants: redrawing Gail's house with classical elements, perverting the original design. Gail's kneejerk protest invites Roark to give a Big "SHUT UP!" to the former.
Dominique deciding to end her marriage to Gail by exposing her affair with Roark in the papers. She knows that the marriage is a sham, especially now that Gail has folded to pressure and she wants to do what's right.
Gail closing the Wynand Papers after he's forced to give Toohey back his job. Toohey does find another position, but he loses that battle.