Literature Map is a handy site that lets you enter the name of an author you know -- and gives you the names of similar authors.
If you're looking for historical fiction:
Historical Novels lists fiction by broad periods, such as Medieval Europe or 20th Century, and breaks it down further into themes such as "The Crusades" or "Europe Between the Wars."
War Through the Generations lists novels set during any wartime period that involves the US, though it's not restricted to US topics.
Have at it, people!
Steve