I was searching through the web for help on this crazy engineering problem which seemed out of the world. Must say there are tons of site out there, but most offer documents, notes, flash notes. I don't understand why someone would want to study from someone else's notes. I love to study and make way ahead on my own. It's only when a nagging problem ends up taking hours that I seek external intervention. Transtutors is that perfect source of a rich collection of Q&A. You would need to search and navigate a while but chances are if you don't find the exact problem, you would find something similar.