Searching for material online saves you a trip to a library, especially if you go to a library for a specific title only to find it is already checked out. Most public and university libraries across the United States have online databases that are updated daily, letting researchers know when a source is available or unavailable. Online libraries like World Cat (see Resources) also let you know which libraries carry the sources you are looking for and how many copies are available.
Finding your sources on an online library and seeing which physical library they are located seems great to begin with, but given the travel lull to retrieve your reference, there is a chance that the available source may be checked out when you go the library. Most online libraries do not allow researchers to reserve books online, so beware.
With the ILLiad Interlibrary Loan system--a system that connects all of the world's libraries in one space--researchers can order books, articles and other research media and have these materials shipped to a local library. Best yet, you can order as many books and articles as you want at one time since there isn't any checkout limit.
However, bear in mind that books and articles ordered by ILLiad (see Resources) may take a long time to ship depending on the book's location, so be sure to order books with plenty of time to spare if you have a research deadline.
Some online library databases charge users to download articles. Online library search engines like JSTOR (see Resources) provide users with free article abstracts or may provide the first page of the text. However, if you want to read the entire article, you're required to purchase the article for personal use. But you can side-step this requirement if you have access to a university library which typically subscribes to these premium library sites.