I have used meritnation.com for Maths and Science only, but the kind of help I got from the website impressed me very much.
My friend had told me about this website and that it provides lot of free notes and stuff, so I went and checked myself. The NCERT solutions I saw were too good and I became a paid member.
Nowadays, homework, and even revision for exam has become interesting. Plus I made a lot of chatting friends on the website too. Good fun after a tiring study session.
There are lots of sample papers, exactly like sample paper books. And the chapters have audio too, which I prefer for studying.