You have already added some of my favorite oldies (Edgar Rice Burroughs & E.E. (Doc) Smith) but I can still provide a few more you might enjoy. I would also have mentioned Asimov, Dickson, Harrison, Laumer, Anthony, Foster, Card, Heinlien, Pohl, Brin and Clarke had they not already been mentioned.
Some not mentioned I reccomend:
Almost anything by Jerry Pournelle.
"Cross-Time Engineer / Conrad Stargard" series by Leo Frankowski
in which a twentieth-century engineer travels back in time to thirteenth-century Poland. The series begins with "The Cross-Time Engineer"
The "Sand Wars" series by Charles Ingrid
which begins with "Solar Kill" (1987)
The "Sten" series by Chris Bunch & Allen Cole
which begins with "Sten" (1982)
The "Foreigner" series by C.J Cherryh
which begins with "Foreigner" (1994)
The "Chanur" series by C.J. Cherryh
which begins with "The Pride of Chanur" (1981)
The "Sam McCade" series by William C. Dietz
which begins with "War World" (1986)
"The Forever War" by Joe Haldeman
The "Rim World" series by A. Bertram Chandler
which begins with "The Rim of Space" (1961)
The "Regiment" series by John Dalmas
which begins with "Regiment" (1987)
The "War Against the Chtorr" series by David Gerrold
which begins with "A Matter for Men" (1983)
The "Small Colonial War" Series by Robert Frezza
which begins with "A Small Colonial War" (1989)
"The Helmsman Saga" by Bill Baldwin
which begins with "The Helmsman" (1985)
The "Mageworld" series by Debra Doyle
which begins with "By Honor Betray'd"
"Chronicles of Gor" series by John Norman
which begins with Tarnsman of Gor (1966)
Sort of overlaps with the Fantasy genre, much as Edgar Rice Burroughs does. The first dozen ot so were great (Of course I read them in college so keep that in mind.) but he must have had a really bad run in with a woman at some point, because the later books take a definite negative slant on women. However, that does not take away from the worth of the earlier books. It is my opinion that the Pern books of Anne McCaffery were likely influenced by the "Riding Birds" of Gor.
The "Callisto" series by Lin Carter
which begins with Jandar of Callisto (1972)
The "Gondwane" series by Lin Carter
which begins with "The Warrior of World's End" (1974)
Some FANTASY novels that you might enjoy are:
"King Kull" series by Robert E. Howard
which begins with "King Kull" (1967)
"Conan the Barbarian" series by Robert E. Howard
The "Horseclans" series by Robert Adams
which begins with The Coming of the Horseclans (1975)
Almost anything by R.A. Salvatore
You did not give a range of OLD so I figured anyone who went back at least 10-20 years would qualify.
More recently in the Fantasy realm I have LOVED
anything written by David Gemmell.