Looking for Difficult Problems for Multivariable Calculus

Hello,

I'm currently taking a multivariable calculus course. While my professor is quite good at what he does, I find the textbook I'm currently using to be too easy. I just took the first of three exams yesterday and found myself overwhelmed with the difficulty considering that I've never had any difficulty solving the problems in the textbook.

So in short, I'm looking for either difficult problems somewhere on the Internet or recommendations to a textbook that has them. I am not looking to 'learn' from the book exactly, as I feel that I understand the material somewhat well. Simply put, I ask for suggestions of anywhere that has good problems to do without regard for the instruction presented.

Also, I wasn't sure if I should post this here or in the calculus specific forum, so if it's not in the right place, just let me know.