Li Si's book of admonition and marching orders, Chao Cuo's on your millet, Wei Zhi's ten thoughts on admonition by Emperor Taizong, Zhuge Liang's model (two parts before and after), Yang Jisheng's book of inviting thieves, Harry's book of admonition and Jiajing, and Sun Jiagan's book of three habits and one disadvantage in Qing Dynasty! It's all classic!

If you want to study further, I recommend a book for you! The Book of Emperors in Past Dynasties is full of warnings from famous ministers in past dynasties, among which the more classic ones are included!