Are you hoping for a futuristic setting(space or advanced city with skylines and ) with a mixture of low- and high-tech gadgets, magic vs science? Or maybe a retro type universe where it's hi-tech gadgets in a low-tech natural, earthen setting? Either or? Maybe neither? Fill in the blank!
Until then here are some that come to mind, forgive me if they are bad examples...
I guess some might say Star Wars is a decent blend of the two, I personally have never read the books though. Clearly they have advanced travel and gadgetry, but two elements involved in the plot are light sabers and the Force. Light sabers are melee weapons which no matter how advanced in construction are not truly futuristic examples of combat. As for the Force it can be seen as a type of magic system.
A mention in a 'similar'(used lightly) vein as Star Wars is Dune. Dune takes place on multiple planets but mostly on a desert planet with political strife between dukedoms over a rare resource. A third lot being low-tech, yet highly skilled and spirited indigenous. There is some combat involving guns and melee weapons, but no magic. There is space travel and some gadgets like force fields but neither heavily influence the book. I HAVE read Dune and I'm sure some will strongly argue with me, but I did not get a heavy sense of science.
I feel H.P. Lovecraft is a blend of fantasy and sci fi. There are fantastical, supernatural creatures of cosmic origin in a low-tech late 19th to early 20th century, almost historical setting. Mentions of otherworlds and dream states. I would say they do actually lean more towards historical horror/fantasy than science fiction, regardless of the origins.
one of my personal favorites is john ringos empire of man series. march upcountry, march to the sea march to the stars. theres a forth, we few, but its pretty much strait up sci fi. the first three deal with a company of space marines stranded on a low teck planet where they are forced to adopt low tech war fighting