To learn a lot about rc cars, what's hot and popular, visit some of the good online forums such as RCTech.net, RCUniverse.com, and Radiocontrolzone.com. I visit these three forums regularly, but for me the best is RCTech.net, which I visit almost every day.
RCTech.net has a lot of helpful members who are experienced in racing rc cars and can give beginners good tips and answers. The forum is well organized and is very popular... post a question and you will usually get a fast answer. Only downside is the site is mostly about rc cars and trucks.
For rc airplanes and helicopters, RCUniverse is a good resource. Topics cover almost everything that is radio control.
And finally, I visit Radiocontrolzone.com mainly because there's a thread on new product release. So if your interested in knowing about the newest, unreleased products, this is the forum to visit.