The NSDA's Debate Training Guide is a short and basic guide that can be useful for newcomers to debate as a topic, helping you to familiarize yourself with its most basic aspects and attributes.
MONASH UNIVERSITY DEBATE GUIDE
Monash University has the most successful debate society on the Australian debate circuit. Its training guide, written by Tim Sonnreich, is freely available online.
This section of the International Debate Education Association’s website allows you to look at motions from past debates by topic or rank (Top 100 Debates) and contains a useful bibliography (links to online articles) for these motions. It can therefore be helpful for your research.
AMERICAN RHETORIC ONLINE SPEECH BANK
This website has a "speech bank" with more than 5,000 speeches, many with audio and video of their delivery, that you can use as a reference for English language oratory by both native and non-native speakers. Of particular note are the site's "Top 100 American Speeches" which, in addition to being examples of highly effective public speaking, will give you a window into American history and culture.
This website, affiliated with Brigham Young University, is a useful resource on classical rhetoric and rhetorical devices.