The most useful books for historical research are unlikely to be available on the web (only books out of copyright are available for free). Check your public library or the WorldCat catalog (on the right) to find them. Or try to get a used copy on Amazon!
Here are some examples of the types of books you need:
Use WORLDCAT.ORG to find books on your topic. WorldCat is an online catalog for all the libraries in the U.S. You can find out which library close to you has the book you are looking for. Enter your topic and other keywords describing what you are looking for.
Examples: Renaissance and daily life
Renaissance and travel guides
Renaissance and encyclopedias
World War II and letters
Golden Rush and Diaries
Always use the ADVANCED SEARCH to be able to limit your search (by date or language for example) if necessary.
When you look at your results, you will be able to locate the closest library where the book is available. You can also search the online catalog of your own public library. If your library doesn't own the book, you can use the "interlibrary loan service" to obtain it.