Just about everyone I know has now read the seventh and (what appears to be) final book of the Harry Potter series by J.K. Rowling. No spoilers here, BTW, because I haven't and probably won't.
No disparagement on the part of J.K. meant there - I have read a few chapters of the Philosopher's Stone, and it seems reasonably well composed. It just happens that there is a wealth of other material I wish to read more.
If, however, you've read it all and now find you want to read some more, let me recommend a few things. Thing one, before I go any further, avoid the Lord of the Rings. You're not ready for that yet. It will just put you off reading again and all that will have been wasted.
The Hobbit - J.R.R. Tolkien
Now, I know I just told you to stay away from one of Professor Tolkien's greater works. However, I do believe if you made it through "Goblet of Fire", you are more than ready for the Hobbit. You will find it a well crafted tale of high fantasy adventure. Elves, dragons (well, just one great dragon), goblins and trolls. Dwarves and treasure. It is crafted originally as a children's tale, and although there is a great deal of back story and legend built in, it does not get in the way of the fun.
Master of the Five Magics - Lyndon Hardy
This is a more complicated read, best introduced to the teenage types. The characters themselves are a bit forgettable, but the system of magic is the real star anyways. Mr. Hardy has taken great pains to craft a very detailed and plausible set of rules for the use and control of magic in his books. The sequels are less entertaining, but feature different characters on different journeys, so are not so very important.
Magician: Apprentice & Magician: Master - Raymond E. Feist
(originally published as a single volume, entitled Magician)
These two novels (or one I suppose if you found it before me) comprise the first portion of what is more widely know as the Riftwar Saga. I consider them among the best fantasy written in the end of the 20th century. They are a bit long taken together, but well worth the effort.
Start with those three recommendations. When you've completed that come back and we'll talk about this - Robert A. Heinlein. It will change you.