I agree with all of the fantastic advice above. Anne-Marie Concepcion and David Blatner are absolutely amazing. They also have an entertaining podcast and blog called InDesign Secrets. This site has amazing tips, podcasts, and videos.
Another amazing reference I give people trying to learn InDesign is Chad Chelius's InDesign Learn by Video. He goes in explicit detail with InDesign. I also like that it is a DVD and I can watch it anywhere without being online.
Terry White has some great tips and trick about InDesign as well. He also has videos on YouTube and Adobe TV.
Deke McClelland has a series on Lynda.com about InDesign.
Classroom in a Book for Indesign is also a good learning tool.
I follow all of them and more and learn something new each day. They are all amazing and I get a different experience with each trainer. Adobe's website has a lot of skilled and talented people trainers who are happy to share what they know about InDesign.
All of these tips and the future ones will help you master InDesign in no time. Have fun learning! 