I had one game world where elves were an NPC race of fey. Ageless and alternately whimsical and cruel, the players referred to them as sharks. They'd be smiling and laughing along with you, and then they'd try to kill you, still smiling. Two minutes later, they'd have forgotten the entire thing, and be your best friend again... Intensely chaotic, and intensely passionate, the Elves didn't believe in lying, or holding *anything* back. If they had an urge, they'd go with it. Forever's too long a time to sit around and think about whether or not something is a good idea. The ultimate extreme action junkies, Elves are all about filling their tedious (and potentially endless, in the vanishingly rare cases where they don't get themselves killed young) lives with moments of excitement, whether that excitement be joy or pleasure or sheer terror or mindless fury, it's all good to the Elf. And if a few mortals get killed in the process? Whatever. They'll just make more...
The Orcs of that setting were more like 3.5 interpretations of Hobgoblins. I noted that they were Lawful, and made them so. Harshly organized and obsessed with personal honor, they ruled grim cities of stone that seemed to just spring up suddenly in lands they conquered, slave-miners, laborers and craftsmen working 24/7 to maintain the Orc war machine. After meeting some, one of the players snarked, 'Wow, Klingon Orcs.' and I snarked back, 'Wait till you meet the Romulan Dark Elves...'
Before the forest gnomes of Termana were added to the Scarred Lands setting, I made up my own Gnomes, the nomadic 'Rus,' who traveled in brightly painted wagons and basically served as the Gypsies of the setting, being tinkers, entertainers, fortune-tellers and self-proclaimed keepers of secret lore. They specialized in illusion magic, to enhance their performances and augment their reputation for having 'tricks' up their sleeves to protect them from abuse at the hands of those larger and more powerful than themselves. They claimed to have a hidden kingdom, that only they could find, and even claimed to have an invisible college of magic, where their greatest secrets could be found by none but themselves. Their more powerful spellcasters tapped into the Plane of Shadow to bring some reality to their fictions, and indeed, there *was* an 'invisible college' of sorts...