You'll need to do some background research first to develop a good speech topic.
Some good places to find background information:
These Library databases and ProCon.org help you find topics for speeches, credible information on those topics, and citations to other credible resources. When you're ready, move on to refining your topic.
Now that you've done some background research, it's time to narrow your topic. Remember: the shorter your speech, the narrower your topic needs to be. Here are some suggestions for narrowing and defining your topic:
Describe and develop your topic in some detail. Try filling in the blanks in the following sentence, as much as you can:
I want to speak on ____(what/who)____
and ____(what/who)____
in ____(where)____
during ____(when)____
because ____(why)____.