There are tons of books lists out there. Seriously, search for "best books for ESL" or "best books for English learners" and there'll be millions of search results. So, here are my disclaimers. This list is, in no way, a definitive list of English classic books. There are other pages for that kind of thing. It's not a list of the absolute best books for students of English (because that's a list that doesn't actually exist anywhere, since book preferences are subjective).
However, this is a list of some good, classic, English books that provide a place to start if you're having trouble finding something to read! Here are my basic criteria that I used to choose the books for this list.
1) Length. Basically, I recommend shorter books for lower levels.
2) Availability. I like free books! And (free) books online are excellent for people who may not have access to a large selection of printed English books.
3) Classics. I went with a very loose definition of 'classic'; generally, I chose books that are either widely read, or at least widely known through some other medium (such as movies).
A Collection of Beatrix Potter Stories by Beatrix Potter
Mr. Bean in Town