Youdebate.com provides debate Topics & polls and is a US site with many US issues covered.  International topics are not so well developed and lack a non-US point of view while some sections will not be used outside the US  (e.g. the whole section on Conspiracy Debates which is utterly useless to anyone preparing for a major competition) however it is still a valuable source of information for many debates.

The Topics covered broadly fall into the following categories:

Conspiracy Debates 
Current event Debates
Education Debates
Entertainment Debates
Environment Debates
Government Debates
Health Debates
History Debates
Politics Debates
Religion Debates
Science Debates
Society Debate