Study and Reading Group Guides are a great way to enhance your reading experience and expose you to new ways of looking at literature. Some of my regularly visited online sites are as follows.
The Novel Guide
Cliffs Notes
Bibliomania
The Literature Network
Penguin
Random House
Oprah's Book Club
Links to online resources for free audio book and complete texts of public domain works (out of copyright)
LibriVox (Audio)
The Literature Network (Text)
Project Gutenberg (Text and some audio)
A Celebration of Women Writers (Text)
bravenet.com