I recently come across this website www.usmlexchange.com
These people have come up with great idea, which is allowing students to share USMLE questions with each other.
The biggest advantage that I have seen over other qbanks, is the ability to rate how good is the question and then you can search for questions that received only 10 stars!
Signing up is free and they won't charge you anything. But then I realized that they give you only 50 credits (which means you can see only 50 questions), later on if you want more question you can either donate to them or post questions yourself so that you get more credit
So guys go and see that website and see if you like it.