For me just the standard, basic Tolkien reading list it seems
The Silmarillion
The Hobbit
The Fellowship of the Ring
The Two Towers
The Return of the King
Unfinished Tales
The Children of Hurin (god knows why I actually bought that, I'd read pretty much everything in it in the Sil and UT!!)
A few years ago I tried the first Book of Lost Tales, but just couldn't get into it, the english was just too archaic, but I intend to try again when I'm off over summer, and I'm going to try for the History of Middle Earth series as well