CliffsNotes offers summaries, book notes and/or study guides for every subject that includes Literature, Writing, Foreign Languages, Math, Sciences with the only exception of art. The list of available items is very rich and it covers both common and obscure topics. If you need help understanding Dostoevsky or preparing for the Military Flight Aptitude Test you can find the study material here.
CliffsNotes’ easy layout makes it easy to use and navigate smoothly. Their Help page offers over 40 subheadings covering everything from the definition of an account with Wiley to taxes and customs. You can opt for email subscription of its newsletter service in a 1-2-3 steps. It also offers to search on the website. The website also offers for shopping its books, PDFs, and other products online.

I give it four stars rating.

Now I'm not totally bashing on CliffNotes, I think it certainly has its place, but it's not all its cracked up to be. CliffNotes may give you a solid and thorough understanding of the fundamentals of a specific topics, but professors in my experience don't test on fundamentals they taste on their own take on the fundamentals, their on flavor of the fundamentals. They also test on nuisances of the material they particularly know or appreciate. That being said, CliffNotes are still important; they can arm you with a preemtive understanding of the material so that in lecture, or as you page through notes while preparing for a test your less worried about the fundamentals and more worried about understanding your professors personal nuisances. So in that case, CliffNotes are valid.
As a current Biology student, I say use at your discretion, and make it another tool in your arsenal, but remember that CliffNotes are not a silver bullet, and will not pass the class for you.

When I was in college, CliffsNotes was all the rage in literature courses. The professors hated it and banned it but we still did it. Now they have a website where you can order the CliffsNotes books or even take advantage of some things for FREE! They have podcasts and multiple choice questions to see if you know what you are talking about before a test. Its just a great site and a great way to help you get through those literature classes that they force you to take without having to waste time you may not want to waste reading a full book. I am not advocating cheating or going against your professor's rules; I am just being honest about things here. I would recommend this site to every student who needs it.