How about this quote from chapter 30? Heck Tate is trying to convince Atticus that it was NOT Jem who killed Bob Ewell. Atticus thinks it was Jem and that Heck Tate is trying to say that Bob Ewell fell on his knife to protect Jem, when really, Heck Tate is trying to protect Boo Radley. It was Boo who stabbed Bob Ewell to protect Scout and Jem, who he has been watching over. Heck Tate tells Atticus:
"I never heard tell that it's against the law for a citizen to do his utmost to prevent a crime from being committed, which is exactly what he did, but maybe you'll say it's my duty to tell the town all
about it and not hush it up. Know what'd happen then? All the ladies in Maycomb includin' my wife'd be knocking on his door bringing angel food cakes. To my way of thinkin', Mr. Finch, taking the one man
who's done you and this town a great service an' draggin' him with his shy ways into the limelight- to me, that's a sin. It's a sin and I'm not about to have it on my head. If it was any other man, it'd be
different. But not this man, Mr. Finch."
This shows that in spite of being a recluse, in spite of being the subject of ridicule, Boo Radley was, in fact, a pretty brave guy when it came to his secret "friends" - Scout and Jem. The reader learns at the end of the novel that Boo has been doing more than just leaving trinkets in the tree stump for Jem and Scout. He has been watching out for them and winds up protecting them from a crazy drunk white trash lunatic, when the rest of the citizens of Maycomb, including Atticus, Heck Tate and the police, could not.
This is a good quote with which to end your essay, since you are at the end of it. You do not need to use the entire quote, though. I think it would be a good one to use to prove that Boo is brave. Many people are underestimated in this novel, and Boo is perhaps one of the most underestimated. He turns out to be the hero -- how about that? It is one of the great ironies of this novel that the person the children have feared the most turns out to be the one who saves them.
Boo Radley's actual saving the children from Bob Ewell is cited in the actions during which Scout narrates as if there is a man she does not know in the action of the story. She reports:
"The man was walking with the staccato steps of someone carrying a load too heavy for him. He was going around the corner. He was carrying Jem. Jem’s arm was dangling crazily in front of him. By the time I reached the corner the man was crossing our front yard. Light from our front door framed Atticus for an instant; he ran down the steps, and together, he and the man took Jem inside."
This demonstrates the man we later come to identify as Boo has just recovered a broken Jem from under the tree that Bob Ewell lies under dead. To cross Bob Ewell, a drunk man with a kitchen knife in the dark, can certainly be considered dangerous.
Another one I like is from Atticus. After Atticus is convinced that Jem destroyed Bob Ewell, Mr. Tate works Atticus over convincing him that Jem couldn't have done it, and that it could look like and accident. However, Tate insinuates Boo's heroism. Atticus finally acknowledges it:
Before he went inside the house, he stopped in front of Boo Radley. “Thank you for my children, Arthur,” he said.