I totally get the struggle of finding quality free epubs. My go-to spot is Project Gutenberg, which has over 60,000 free ebooks, including many classics. The interface is simple, and everything is legal since they focus on public domain works.
For more contemporary titles, I sometimes check out Open Library, which lets you borrow ebooks like a digital library. Just remember that while some sites offer free downloads, they might not always be legal. I avoid sketchy sites because supporting authors is important to me. If you're into indie authors, many offer free epubs on their personal websites or through newsletters as a way to attract new readers.