Don't forget about Google! Google Scholar in particular can be very useful if used to its fullest potential.
Click here for a brief tutorial of how best to search in Google Scholar.
A small selection of E-books from WMU Libraries:
Use the WorldCat databse to identify books on your topic. WorldCat included books at WMU as well as other libraries throughout the country. Use the interlibrary loan system to request delivery of books to your address.