Philotomy’s OD&D Musings This web site has Philotomy’s comments on and house rules for Original D&D (the three little beige booklets, their supplements, and the Holmes Basic Set). There’s also a great campaign writeup on his Lost City campaign (based on module B4).
Solstice This is a TiddlyWiki site with house rules for Sham’s OD&D campaign. You can even download a copy of the Tiddlywiki and its rules to use on your own system.
Classical Dungeons & Dragons
OD&Dities An archive of the 12 issues of the excellent Classical D&D magazine, OD&Dities. While the name implies Original D&D, most of the articles and adventures are for Classical D&D.
The Vaults of Pandius The “official” Mystara web site with lots of information on TSR’s Known World/Mystara campaign setting for classical D&D.
Dragonsfoot “Here at Dragonsfoot you will find more free, quality and original First Edition AD&D resources than anywhere else on the net. Available here are new Adventure Modules, Gaming Worlds, Character Classes, New Monsters, Articles and much more. If conversation about your favourite roleplay games are more your scene, then take a trip to our forums, here you will find the distinctively friendly Dragonsfoot atmosphere where lively and informative chatting and sharing of ideas occur.”
The Delver’s Dungeon “This is the Delver’s Dungeon, a first edition Advanced Dungeons & Dragons ‘fan-site’ filled with old-school gaming goodness.”
Knights & Knaves Alehouse “This board unashamedly and proudly supports Old School GYGAXIAN games. Specifically: Original Dungeons & Dragons – the little books, First Edition Advanced Dungeons and Dragons, and Judges Guild products for OD&D & AD&D. This board is for the discussion of OLD SCHOOL style games and gaming. We make no excuses and no apologies for other game systems not being supported here.”