A good place to start:
Grant Resource Center (GRC) -our membership allows access to a really helpful search tool. The opportunities posted (federal and private) are generally ones you can count on to be repeated. Thus a grant opportunity that closed 2 months ago is still worth a look, it will likley be offered again when you are ready for it.
Other helpful links
Planning to apply for an external grant? CLICK HERE for information on the Ferris approval system.