The standard, classic races. (and variants thereof)
Possibly adding in some from the 3e FRCS, like Aasimar, and tiefling. (with THAT flavor, not the 5e kind) If we're in the Realms.
The monster races, anthropomorphic animals, warforged, odd Spelljammer races etc are excluded intentionally.
That helps foster the sort of feel I want for my campaigns. The newer players are mainly our kids, and their friends. They grew up listening to our war stories of the heady days of AD&D, so I'd like to give them an opportunity to experience that sort of game. Whatever system we actually use. Having 2 humans, a drow, a halfling, a gnome- and OCTOPUS MAN!!!(tm) Is just jarring...
I do a similar thing with classes. Limiting them to mainly the classics. 5e PHB subclasses are totally acceptable. I opt not to use multi-classing or feats. This is to encourage players to play their character- and adventure AS the game. Rather than focusing on "builds" and expoiting the rules for max gain.
Others are more than welcome to do it the they like-when it's your turn to DM, of course. (and if you do choose a totally different list/feel, so much the better! More variety is great it'll help make each campaign stand out!)
As for what all populates the world? The MM+ Volo's, plus some surprise "WHAT the %$#@ is THAT???!!!" 's I pull from my extensive collection of monster books. Just to occasionally ratchet up the pucker factor, and throw off the old, experienced hands.