To be fair, I've only just started using this site... and only for my Vector Calculus class... that being said, it has the textbook we use and solutions to the odd problems for free. For a small fee ($5 a month), you can join and get access to the even problems as well.
For me - this is a life-saver! Our prof only assigns problems from this text, and having the solutions is obviously helpful. It doesn't show each step, but gives you the start and end point, which means you know how to get started and where you should end up.
I'd recommend this to anyone... you can search the texts in it's library before joining, so you know if it'll have your textbook!