There seems to be a general consensus among Tolkien fans that there were 3 'Great Tales' (with good reason, I might add; see
Atanatarion):
1) The Tale of Beren and Luthien (i.e.
The Lay of Leithian)
2) The Tale of the Children of Hurin (i.e. the
Narn)
3) The Fall of Gondolin and the voyages of Earendil (which are actually grouped together by Tolkien in most cases, I believe)
However (and this has been bugging me for quite some time), I distinctly remember Tolkien laying out 4 'Great Tales' somewhere - but I can't remember where!
My best guess is that the 4th tale had something to do with either the 'Wanderings of Hurin' or most likely with Dior and/or Nauglamir.
Someone please help!