There are many different types of information. You probably will need a combination, but look over the categories below and decide where to focus your energies.
It often saves time in the long run to look at an encyclopedia article on your topic. Major ideas and facts will be given, and when you look at more specific sources later, you will have a better understanding of which ones are more significant.
Librarians know good sources of background material for topics, so ask.
Any research project is stronger if hard facts -- statistics, formulas, budget figures, etc. -- are included.
Reference sources (both books and on-line) are the most likely places to locate these (although they will show up in almost all sources). Check out this site on Statistics on the World Wide Web.
Although these are totally separate concerns, they are most likely to show up in the same places: periodical articles and the Internet. These sources are quickly updated and often focus on specific places and issues. Individual's opinions are often stressed, whereas other sources usually have a broader perspective. (See the Study Guide Finding Periodical Articles.)
For projects that require a deeper knowledge of a topic, books and scholarly journals are generally the best sources. They are longer than the sources listed above, and they are usually written by experts. (See the Study Guides Finding Books and Finding Periodical Articles.)