Not an anarchist anymore, but from back when I was, I know that there are a number of anarchist critiques of Engels' On Authority. This is where you'll find a lot of contemporary anarchist thought on the concept of authority as a deliberate counter to Marxism.
Of course, it goes without saying, I disagree with these critiques, but if you want to expand your knowledge of leftist theory in general, Read On Authority seems to be one of the more popular critiques of Engels from anarchists, and the Anarchist FAQ in general is probably the single-most comprehensive source for beginners to anarchism today.