Since most test prep companies on this site will state that their course is the best for self study, I'll start things rolling by directing you to our 500+ video (35-hour) course, which happens to be 100% free.
You can also use our course in conjunction with Beat The GMAT's free 60-Day Study Guide (
https://www.beatthegmat.com/mba/gmat-guide). Each day, you'll receive an email with a series of learning activities that guide you, step-by-step, from Day 1 to test day. This will ensure that you will cover everything that the GMAT tests.
Here's an outline of all 60 emails:
https://www.beatthegmat.com/mba/gmat-guide-outline
Cheers,
Brent