Anyhoo- 1st published D&D modules. I don't own but have looked over the (extremely rare and pricey) originals. Great looking maps and art by Brad S. (AKA Morno) of Arduin fame.
The Misty Isles would a be a great tie- in with the new Seafaring section in GoS.
If you strictly mean an OSR D&D style game? Depends on the mood and game play desired-
S&W Whitebox when I want to make my own detailed house-ruled variant
Iron Falcon when I want to adhere as closely as possible to my LBB days
But for an edition of D&D? Moldvay/Cook/Marsh B/X sets.