I really liked the "Mars" novels by Edgar Rice Burroughs. He also wrote a series set on Venus. And, I understand that there are similar books (swordsmen in space kind of adventure) by Otis Adelbert Kline. I'm pretty sure all the available books are in the MobileRead database.
ePub format:
Burrough's Barsoom Omnibus, prepared by Harry T
Burrough's Venus Omnibus, prepared by Harry T
Kline's Venus Omnibus, prepared by mtravellerh
MobiPocket format:
Burrough's Barsoom Omnibus, prepared by Harry T
Burrough's Venus Omnibus, prepared by Harry T
Kline's Venus Omnibus, prepared by Harry T