Genres are listed in the sidebar under 2012 Nominations by Genre -- just click on the category for the latest list of nominated titles. Titles are added continuously until October 15th, when public nominations close, and eligible publisher-nominated titles will be added after that.
Here's the form again. It'll be kicked back to you if you try to nominate more than one book per genre, or if the book's already been nominated by someone else. Enjoy!