For me... The choices are simple. It depends on the campaign world I'm playing in, and since I make my own campaign worlds, it has varied greatly. However, my most common choices are...
Human: Simple, and easy to incorporate 99% of the time.
Elf: Also simple, as well as classic. Plus, I have half-decent player who won't play any other race... period. (Should change that... kill his current character, and have him resurrected as a Gnome, or a Dwarf. speaking of...)
Dwarf: Never used by players, but always featured heavily in the over-arching adventure some how.
Halfling: Usually used by some player, usually as a fighter, cleric, or monk (surprisingly never a rogue, though).
Gnomes: My personal favorite race, and like Dwarves, hardly ever chosen by a player, but featured often in my main adventure somehow.
Orc: Never big evil dumb brutes, but more traveling nomads, who don't have a place to call home. (I blame elder scrolls for this... rather, I thank elder scrolls for this.) Though, I do homebrew away the -2 wis that they they have naturally.
HobGoblins/Goblins: Though never chosen, I leave the choice open, because I always hear my players talking about interesting ideas that they want to do with a character of these races, and I'm hoping that one day they will.
Half-Races: Half-Elf and Half-Orc are just the top of this list. I've created a Half-Dwarf, a Half-Halflings (called Quarterlings by the group), and a Half-Gnome (which are actually pretty neat, if I do say so myself.) Now, I'm sure someone else has created half races before, but they were some of the first things I ever homebrewed, and they have changed a bit over time, so they fit more in line with the other races.