Ebook Collection has several books that will provide information on WWI topics. Specifically, take a look at:
The Gale in Context: US History database has resources of all kinds that will be useful for this project.
Check out:
World War I and America Topic Center
African Americans in World War I
Case Overviews: Sedition and Espionage in the early 20th Century
History in Dispute is a collection of books that provide multiple viewpoints on historical events. Here are some from World War I that may be useful:
Another good database for any topic is Proquest Central Student. Search by keyword and limit by type of article and date.