LOTR... Of course, since this is really the start of the genre as it exists today. So when you read it and think that it's full of tropes... Continue thinking a little bit and realize that LOTR CREATED those tropes.
The Belgariad by David Eddings. I'll come out and say it, David Eddings was a horrible person, but this series is worth reading. He's dead now so you won't be supporting him if you get these books. The followup series "The Mallorean" is not a must read, it's basically a retread of "The Belgariad". As are his later series "The Tamuli" etc...
The Cosmere by Brandon Sanderson. A lot of people will recommend Mistborn, or the Stormlight Archive, but both of those series are just parts of a greater arc called "The Cosmere". I would recommend starting with Elantris or Warbreaker, both of which are standalone books, but are in the Cosmere. Then go to Mistborn series 1, then tackle Stormlight Archive. Be warned, each book in SA is longer than LOTR in its entirety. But it's well worth the read.
A Song for Arbonne by Guy Gavriel Kay: One of my wife's favorite books. Not a series, but worth the read.
Memory, Sorry and Thorn by Tad Williams: Excellent series that doesn't get the recognition it deserves.
Destiny's Crucible by Olan Thorensen: I liked this one a lot and continue to follow it, although it's starting to get a little long.
The Riyria Revelations and Chronicles by Michael J Sullivan: Both of these series are great and worth the read.