Baen Books
Baen Books are a long established publishers of science fiction and fantasy, much of their back catalog are available to download for free including works from authors such as David Weber, Mercedes Lackey and David Drake.
Beyond This Horizon
Brothers in Arms
Cetaganda
Code of the Lifemaker
Ethan of Athos
Falling Free
Memory
Podkayne of Mars
Realtime Interrupt
Rockets, Redheads and Revolution
Sunrise Alley
The Genesis Machine
The Proteus Operation