1. Look at the very end of chapter 9 (our versions of the book are probably different, so page numbers won't be the same), when Atticus is talking to Uncle Jack about the trial. He states,
"I hope and pray I can get Jem and Scout through it without bitterness, and most of all, without catching Maycomb's usual disease. Why reasonable people go stark raving mad when anything involving a Negro comes up, is something I don't pretend to understand."
In this quote, Atticus is saying that he hopes that he can set a good example for his children as he defends Tom Robinson, and that by setting that example, they can grow up without being racist. He says that normal people just go crazy and act completely irrationally when it comes to black people--racism is a disease that alters judgment, kindness, logic and decency. In chapter 16, when the mob comes for Tom, and Scout talks to Mr. Cunningham, we see this concept in action, so check out that chapter for some more quotes.
2. When Jem is asking Atticus about the things that Mrs. Dubose said about him, one of the questions is whether or not Atticus is a "nigger-lover" like Mrs. Dubose claimed to be. Atticus responds, "I certainly am. I do my best to love everybody." This quote is about 4 pages before the end of chapter eleven. This quote is short, but very important, because it relates Atticus's entire attitude about people--not only black people, but all people. He says that he strives to love everybody, despite their appearances, station in life, background, or class. And, he does a pretty good job of living by that standard in this book.
3. About four pages into chapter 12, Cal has brought Jem and Scout to her church, and Lula protests them being there by saying,
"You ain't got no business bringin' white chillun here--they got their church, we got our'n."
Here, we see a bit of discrimination coming from the black side of the issue; Lula doesn't want white people coming into her church, just like white people don't want black people coming to theirs. This quote is significant because it shows that racism exists on both sides of the aisle, and that all people are subject to its meanness. Of course, most of the people at Cal's church were very nice, but Lula showed how racism can exist in all forms.
There are just so many quotes that could be used, and these are just a few; I am sure that other editors will have some great ideas too. I hope that they helped a bit; good luck!