Sometimes the hardest part about getting started is finding a topic to talk about. Here are some resources where you can browse through subjects and get some basic information.
If you have a topic in mind for your speech but aren't sure where to find information about it, start with these resources. You can search a number of different dictionaries and encyclopedias at one time in these three databases. Some individual sources that might be useful are listed under Dictionaries and Encyclopedias.
These are some specialized dictionaries and encyclopedias that might be useful.