Best sites for study guides/practice tests for CDL?

I won't try to depress everyone with the story of why I'm in this situation, but I'm looking to get the best resources to practice for a CDL. I'm in the process of learning but already have a driver to drive a Pete that my Dad left behind. Not that I'm in a hurry to hop behind the wheel, but I rather get the testing over with to have some time under my belt with it. If you know of any good sites, please let me know. I've been doing some searching but haven't really found any good material for a beginner with almost no knowledge of this industry like myself. My goal is to keep this truck hauling Hazmat like it has for many years. Thanks in advance and hope to hear from you guys/gals soon.