Offensive Security courses
Offensive Security is really well known in the Penetration Testing community. Their Penetration Testing with Kali Linux (PWK) course and the certification that comes from passing the PWK test, Offensive Security Certified Professional (OSCP), is considered by some to be a "must".
Before I found a job as a red teamer I used to believe this: {Must take. Must pass. Must have that OSCP certification.}
Visit their website at https://www.offensive-security.com/ for a complete list of courses offered.