Scholastic.com probably has one of the best book knowledge Harry Potter quiz. The Harry Potter: Wizard Challenge Trivia allows you to choose which of the seven books you would like to be quizzed on or you can be quizzed on all of them at the same time. It us multiple choice and you are only allowed to get three wrong answers before you will have to start over. The answers are based on the books not the movies, so you need to make sure that you have read them. For a link, see resources below.
theallmightyguru.com has a Harry Potter Sorting Hat House Quiz that will put you in one of the Hogwarts houses (Gryffindor, Hufflepuff, Ravenclaw, or Slytherin) based on your answers to their multiple choice questions. Some of the questions are obviously for the younger crowd, but it can still be fun for an adult Harry Potter fan. See resources below for a link.
MSN even has a Harry Potter quiz to test your knowledge. It is a short multiple choice quiz that covers a lot of Harry Potter trivia including a question on if you can name all of the Weasley children in the correct birth order. See resources below for a link.
MuggleNet has an entire page of Harry Potter Quizzes that are rated from "pretty easy" to "very hard." The "very hard" are difficult enough to sump even the best of the well read Harry Potter fans. This sight is highly recommended. See resources below for a link.