As I first read the Labyrinth Lord rule books, and began to conceive the campaign I'd like to run, one of the first decisions I made was to ditch hobbits and to reskin the halfling class / race as rat people. This simple change has worked out marvellously, and has really helped to add a bit of unique flavour to the setting.
I've been thinking recently about the word "halfling", and its possible use for a whole swathe of other half-sized folk, some of whom could quite possibly be adventurers.
Similarly, I thought that the standard halfling class or race could easily be used for these other races, perhaps with a slight tweak to give each of them some unique ability. So, mechanically speaking, the halfling races have all the abilities granted by the standard LL halfling race or class, apart from the hiding ability, which is replaced by a unique racial ability as described below. I have also given them all infravision, as they usually dwell underground.
Rat-folk: Humanoid rats, complete with fur, tails and twitchy noses. Actually do have the hiding ability (as per hobbits), which works 3 in 6 in any environment.
Kobolds: A diminutive race of snivelling dog men. Tend to hang out in packs. Kobold adventurers have the ability to track with their excellent sense of smell. In my campaign, kobolds are a wretched and cowardly race, although intensely loyal to their companions. Although their respect for other races is minimal, among themselves they tend towards lawful alignment. Their societies display the full range of good and evil, similar to any human culture.
Goblins: In my campaign goblins are a fey race (the same as elves), meaning that they originate from a parallel dimension, where they typically spend most of their time. Some however may become adventurers and choose to explore the physical world. As a special ability they know additional languages (the tongues of fey elves and pixies), can identify dimensional portals, and are 90% immune to charm effects. In my campaign, while goblins are mischievous and tend towards chaotic alignment, unlike the standard D&D goblins they are in no way inherently evil.
Deep gnomes (svirfneblin): Yet to be specifically encountered in our games, but having been referred to, this race dwells in deep subterranean caverns, and are sometimes encountered by the dwarrow as they delve for metals. They have the ability to know their depth and orientation underground, and to detect sloping passages. These abilities work 2 in 6 of the time. They also speak the tongue of the dwarrow.
Forest gnomes: A meek and homely race, unlikely to produce much in the way of bold adventurers. Nevertheless, if such an individual were to exist they would have the ability to speak the languages of burrowing animals, and a 2 in 6 chance of detecting decrepit or unstable structures underground.
Note that all of these races have the standard restrictions of the halfling race, as regards to minimum / maximum ability scores, and level limits.