You can download any paper from ACM for free, until June 30, 2020! Quickly grab what you couldn't even find on sci-hub!
Don't know what to read? The Computing Surveys journal is full of papers that give an overview to the state of the art in many topics, it's always a good way to discover new problems, challenges and solutions: https://dl.acm.org/journal/csur
Yo, there’s also Library Genesis for textbook PDFs. It’s fucking great.