We discussed the importance of having diversity not only among the secondary characters in YA but with the main characters as well. More and more readers are interested in seeing their 'face' in the story. The idea that the default for a main character should be 'boy' (as the books I grew up reading seemed to be) is losing strength at last. The popularity of The Hunger Games demonstrated that boys would read stories with girls as the main character. The idea that the default for a main character has to be white and straight should be the next to go.
Megan Crewe related how she was told by agents how her manuscript, set in Japan, would be difficult to sell. Esther Friesner's Spirit Princess and Gloria Oliver's In the Service of Samurai are both set in Japan with Japanese main characters, so perhaps that is changing.
People of color as main characters have begun appearing in YA, but there have been reports bookcovers were changed to depict a white character. Justine Larbalestier's Liar, Cindy Pons' Silver Phoenix and others have been affected this way. This might be due to a marketing decision, but more people need to speak out against it.
LGBT characters have begun to appear as secondary characters, but there needs to be main characters as well. Cheryl Rainfield's Scars has such a character. Her recent blog is about the World Fantasy panel and (as she promised at the panel) she has provided a link to books with LGBT characters.
Religion has also been addressed in recent years. YA and middle grade books such as the Percy Jackson series, the Goddess Girls series by Joan Holub and Suzanne Williams, Darkness Rising Book One of the Catmage Chronicles by Meryl Yourish, Hereville: How Mirka Got Her Sword by Barry Deutsch, and Vessel by Sarah Beth Durst have main characters from nonChristian religions.
There were many excellent questions from the audience. Some were from readers trying to find books with diverse characters while others were from writers interested in creating diverse characters.
For the readers, finding these books are not always as easy as going to a bookstore. Some bookstores still have YA as a general catchall, with YA paranormal shelved with YA sports. Big bookstores like Barnes and Noble have subcategorized YA, which may benefit browsers, but not those looking by author's last name. Books with people of color sometimes are misshelved in cultural studies. The advantages of ebooks are that many are searchable by tags, but often readers have to rely on lists on the web (such as provided by Cheryl Rainfield above) to find titles.
The writers in the audience wanted to know how to write about different cultures respectfully. The example was brought up of books where the only person of color was the villain. Points the panelists brought up were that stereotypes are still not the way to go. The more diversity you have in your book, the better. But having diverse characters in your book doesn't mean that your story has to be about discrimination or prejudice. You're just creating a more realistic world.
If you're worried about being accused of cultural appropriation, as long as you have researched the culture, talked with people of that culture, treated it respectfully, and, if possible, found a beta reader to make sure you haven't made any missteps, you've tried your best.
You don't want to have your story be a checklist of some kind, or a message or mission book as that will turn readers of any age off. No one likes to be preached to. There will be times when, due to your story's location or time period, that your characters may need to be from one race or culture. But if they don't, do all your characters - even the walk-ons - have to be white and male?
The panel also brought up the benefits of small press for those having problems finding a market for books with diverse characters. Small press and ebook publishers are willing to take chances on stories with new and diverse voices.