With a setup like that, my knee-jerk suggestions would be:
Gnolls: Proud warrior race guys. They might not necessarily have evolved from hyenas due to exposure to arcane radiation, but their society has grown out of scavenging from some particularly choice ruins - or a fallen "starship" (if of the Spelljammer variety). Matriarchal neo-barbarians who wield energy bolt-launcher "bows" and las-bladed spears.
Aranea: If there's an element of spelljamming in this setting, you could have them be stranded aliens, forced to rely on their shapeshifting to protect them as they integrate into host civilizations. They may even control the nation-state that is the best at airship production, part of their generations-spanning plan to recreate the arcanotechnology they need to return to the stars.
Chitines would be an alternative, more degenerated take on the idea, but that angle is probably best left to more grimdark interpretations.
Shardminds and/or Warforged: Ancient creations of the lost civilization who live on in their wake. Shardminds could be artificial counselors, or the now-fragmented remains of some vast magical artificial intelligence network. Warforged could be the remnants of mekanikal armies.
Nagpas or Devas: Could represent all that remains of the lost civilization (or one of them, at least); too few to preserve what they had, but blessed with the chance to guide the young races in their wake - or cursed to watch the inept fumblings of inferior inheritors.
Lizardfolk or Dragonborn: A once-mighty empire that blasted itself back to savagery, but which is on the rise again, to fit the noblebright motif.
Lupins or Rakasta: A vibrant, energetic, rising young star amongst the nation states. Mystara had faux-French swashbuckling paladin lupins and samurai rakasta on the moon who rode flying sabertoothed tigers. Just think about it.
That's just a handful of ideas, but I could suggest more if needed.