I have the offical act prep book for practice tests/questions. All I need now is to learn the concepts :p.
What score range are you aiming for?
These are the books that I believed helped me the most in scoring a 34, along with taking practice tests:
The Complete Guide to ACT English -Erica Meltzer
Ultimate Guide to ACT Math - Richard Corn
I wasn’t a fan of Barron’s or PR because the explanations were lacking. These books were very thorough and helped me tremendously with understanding the concepts.
Erica Meltzer offers a guide to ACT reading also. I didn’t use it because reading is one of my better subjects, but judging from how great her English book was, it should also be great.
Prepscholar offers a really good blog that recommends ACT books (it’s how I found these). Let me know if you have any more questions!