Of course, this got me thinking about what makes a classic. About a year ago, BookWitty had an article entitled “What Makes a Book a 'Classic'?” by Daniel O'hEidhin. He quotes Italo Calvino’s 14 definitions of a classic: https://www.bookwitty.com/text/what-makes-a-book-a-classic/572f8474acd0d06f852d920f.
If you’re interested in ancient classics, this list might appeal to you: http://www.telegraph.co.uk/culture/books/10610334/15-best-classics-books-of-all-time.html.
If you like more modern classics, you can try the 99 Classic Books Challenge: http://www.listchallenges.com/100-classic-books-challenge.
Personally, I prefer this exhaustive list: http://thegreatestbooks.org/.
And the Top 100 Works of World Literature compiled by the Nobel Institute is really interesting. One hundred authors from 54 countries were polled on what they considered the “best and most central works in world literature”: http://thegreatestbooks.org/lists/28.