There are many open access providers of ebooks. It is always worth a quick google search to see if the title you are looking for is freely available on the web (most often older titles).
WCU Special Collections in the Internet Archive
Digitized WCU catalogs (undergraduate and graduate) back to 1871; yearbooks; books by Russell L. Sturzebecker
Electronic Literature Collection
Published by the Electronic Literature Organization, Maryland Institute for Technology in the Humanities (MITH). Volume 1 includes a medley of recent works of varied forms.
Google Book Search
Google is providing access to books through the Library Project and Partner Program. Not all books are completely available; access may be limited to the book's table of contents and selected pages.
Find free eBooks for your PDA, iPod, eBook reader or cellphone.
[The] Online Books Page
Search over 30,000 free books on the Web, by author, title, or subject.
Thousands of volunteers have provided the free ebooks in this groundbreaking project which now provides over 125,000 titles through their catalog and their affiliates.
A partnership of academic & research institutions, offering a collection of millions of titles digitized from libraries around the world. Use the "full view" option when searching to get full text items viewable on line.
The Chester County Library System (CCLS) of public libraries has many popular fiction and non-fiction e-books as well as audio books you can access online. As a student or employee of West Chester University you can easily get a card even if you do not live in the county. There is a library in West Chester and the main system library is not far, adjacent to the Exton Mall.
If you live outside the county don't forget about your own local library!