While everything you need to know to pass the CCNA exam is online — somewhere — you’re going to want to pick up a book or two.
The CCNA Official Exam Certification Library by Wendell Odom contains the ICND1 and ICND2 official certification guides and is probably the most popular of the CCNA certification books. Others like Todd Lammle’s Cisco Certified Network Associate Study Guide better.
Which one you pick is totally up to you — for the most part, they cover the same material and either will serve you well. This site isn’t meant to replace any existing materials, but to expand upon them.
If you’re enrolled in the Cisco Network Academy, the materials that you already have should be plenty. You can buy one of the books listed above if you want to, but it’s probably not necessary.