The Andre Norton freebies at Amazon:
Project Gutenberg: Star Born, The Defiant Agents, Key Out of Time, Plague Ship, The Time Traders, Storm over Warlock, All Cats are Gray, Star Hunter, Rebel Spurs, Voodoo Planet,
Ride Proud, Rebel!, The Gifts of Asti, The People of the Crater, Ralestone Luck
Baen Free Library: Star Soldiers, Time Traders
Premiere Publishing: Sargasso of Space
Only the last one is free for a limited time. The rest are available for free as ePubs at the linked sites.