The seed races are a group of titan-created races.
Known or possible seed races
These half-giants once had a prosperous society, but around the great sundering they had disappeared. However, they suddenly reemerged when the Horde and the Alliance went to Northrend. Several sources (eg. Sjonnir The Ironshaper) indicate they were indeed once instated by the titans, as there still are metallic vrykul. It is said that the curse of flesh in these beings resulted Azotha as by product, who in their turn evolved into humans.
Earthen were created by the titans to shape the earth. These creatures survive to the present day and have created what would become great ruins of Ulduar, Uldaman and Uldum. They are the distant ancestors to the dwarves, which still prefer the seclusion of the mountains.
Mechagnomes were created by the titans to serve as mechanics of sorts to maintain the enormous databases of the titans, which hold all information about Azeroth and its creatures. They are the ancestors to the gnomes.
Quite recently Gearmaster Mechazod got reawakened by the gnomes of Fizzcrank Airstrip. This particular NPC still has its metallic shape and wants to lift the curse of flesh on all the gnomes as it is inferior to the metallic form they used to have.
Many of the giants on Azeroth were created by the titans as part of their ordering of Azeroth, meant to protect and oversee the land and ocean. During the Burning Legion's first invasion, nearly all of the giants were destroyed, and now only a handful remain in the most untouched areas of Azeroth. To this day, while most of them are still fulfilling their ancient duties, some of them, like molten giants and Baron Kazum, seem to serve the Old Gods against their will.
The tol'vir are a race of "stone-like cat people" created by the titans that originate and dwell in the ruins of Uldum. They were created to maintain titan repositories and machinery. There was once another society of tol'vir in Northrend, but they were overthrown by the nerubians and transformed into Obsidian destroyers. It is possible that some of the original tol'vir in Northrend still exist deep within the remnants of Azjol-Nerub. The tol'vir in Uldum seem to be somehow connected with Al'Akir and his elemental minions.