If you want to get 'old school', you might put the Flan tribes in Greyhawk in this category. In the Forgotten Realms, that honor goes to the tribes of the Shaar.
It's a little bit of a stretch, but aside from the Horde (which was pretty awesome) there was also the Viking handbook from 2nd edition. Not so much on the "nomadic" side of things, but lots of great ideas that nomadic cultures are likely to have. I'd say they were more of a raiding culture.