For the works of classic literature there are many free download options. Those that are well-formatted really stand out.
If you need an epub of one of Shakespeare's plays (for example) I would recommend a visit to Feedbooks. Their files are presented with nice covers that look good together as a set. They are formatted simply, but effectively, making it easy to read a play.
Here are a couple to illustrate:
http://www.feedbooks.com/book/2990/a...-night-s-dream
http://www.feedbooks.com/book/2935/macbeth
Feedbooks offers many other public domain works. Their site would be the first resource I would suggest to students who need epub literature files for course work.