Probably the premier portal for information, both free and otherwise. There's a couple of things that make this website great.
This site has a boatload of free content and they continually add more articles and videos. If your questions can't get answered for free on this site, they probably can't be answered for free.
The new landing page for this site makes it a little tougher to find anything but their services and for-purchase content. They offer resume reviews, case interviews, and a bevy of other resources to get you started. A lot of their for purchase content will be available to you once you come to Kenan-Flagler but if you want to get a head start this is the place.
This is the site of Victor Cheng, author of Case Interview Secrets. You can sign up for his free emails and peruse the many articles he has listed. His site almost serves a bit as Q&A for all things consulting and is a little bit scattered in terms of layout. He's got a sidebar with his most popular articles which are worth a look and he's got a quick video on the 5 biggest resume mistakes.
His Look Over My Shoulder series (LOMS) is an incredibly popular resource for people wanting to really understand what a consulting interview is like.
He also offers resume and case prep services, like a lot of the other top vendors in this space.
Not to be outdone by Victor Cheng, casequestions.com is from Marc Cosentino, author of Case In Point. There are a few interactive cases that you can go through on this site and a few market sizing questions as well. These are really structured to give you a taste of what's behind the paywall rather than truly help you prepare for case interviews.
After sampling his interactive cases and questions he has a number of different options for purchase but it really revolves around the interactive cases. You get access to all of the cases rather than paying case by case but you are limited in how many days you can access. The more days you want to have access, the more expensive the option. It's a great idea and resource if you don't have a case buddy but it also falls short of mimicking a true one-on-one case setting.