I do not know any which fits your terms, really, but if you want some free (and DRM free) SciFi and Adventure book of the more pulpy kind, you can try Baen free library -
http://www.baen.com/library/ Edit - Hmm... seems to be some changes over at Baen:
"The Baen Free Library is undergoing a transition. As a result of our decision to sell our titles at third party vendors, we have had to remove some titles. Others are undergoing alteration and will be brought back into the Library over the next few months. The Second Editions with new material will be available for sale at all venues; the original editions will be restored to the Free Library. We are trying to keep as many titles here as possible. We will also be adding new titles soon, including ones by Larry Correia, and Sharon Lee & Steve Miller."
(
http://www.baen.com/library/intro.asp)
It had a nice good library before, I have more than 70 books from them on my Kindle...