Before I start my April posting on Basic/Expert D&D (I've settled on a methodology that will work well, I think) here are a list of useful rules and ideas scattered on the internet that I will take advantage of, but not repeat because the sources are already good enough:
Gnomes as playable Racial Class - done extremely well by Tim Brannan at The Other Side Blog.
Minotaurs as a playable Racial Class - done right here by me.
Orcs as playable characters - right here, also by me, but also available in the Orcs of Thar Gazetteer (not yet in PDF format, alas)
The Grey Matter Bestiary - written by Leonaru, this is the single greatest free bestiary on the internet and works great with B/X D&D.
Paladins, Rangers, Monks, Druids and other Advanced Labyrinth Lord Fun - The Advanced Edition Companion to Labyrinth Lord makes these all perfectly functional optional races in D&D B/X, so you don't need to wait till you're high level to be a paladin or druid, for example. I won't assume these are classes in the April event, but as a DM I would allow them as options to interested players if pressed upon.
Things I'd like but can't find evidence of, so may have to design on my own:
Hutaakans as playable characters - I seem to recall these existed as a thing at one time, possibly in the Hollow World setting. Does anyone know if proper hutaakan racial classes were ever presented?
Elven Thief racial class - a vital requisite to playing wood elves, in my opinion. I will construct a specific racial class for this purpose at some point if I find the time.
Lupins, Tortles and possibly even kobodls deserve racial classes, too....