The Lord of the Rings - JRR Tolkien. Hands down my favorite book of all time.
Another one...hmmm...the "A Song of Ice and Fire" series by George RR Martin is pretty darn good too.
I have to applaud your choices, although the question was which books, and you listed 2 excellent series... Actually I think it is becoming more and more difficult to pick just a single book. So often authors are writing books in a series instead of individual novels. Even some books that can be read outside of reading the rest of the series (eg Anne Rice's
Interview with a Vampire) by read the other stories in the series can give even more background stories to the major characters.
If I had to choose just solitaire novels, I guess it'd have to be Steven King's
The Stand and
The Golden Key written by a trio of authors: Melanie Rawn, Kate Elliott, and Jennifer Roberson. Oh, and if you happen to read
The Golden Key, make sure you listen to Norah Jones'
The Painter's Song. It puts a haunting meaning behind that song and completely changes what you feel about it. The first time I heard it was after I had read the book, and I got goose-bumps listening to it; I actually thought that if the book were ever turned into a movie, then that would have to be the song used in the opening credits.