Lets see.....
First i feel i have to toss up ANY Rodger Zelazny, he is a mix of scifi/fantasy but its done so well as to be a genre of its own, and well worth reading. Check out something like Lord of Light or his 9 Princess in Amber series. So basically i pimp him out any chance i get because...he is one of my favorite authors period.
Since you have listed Asimov and Clarke id also toss out Heinland(considered one of the fathers of scifi) Stranger from a Strange land is an amazing book, and easily my favorite of his. (though their are a number of other great books he has written)
Joel Sheppard is a relatively new author but i enjoyed his "Cassandra Kresnov" series and its definitely sci-fi, and reasonably well researched.
I <3 to death all of Elizabeth Moons books, she writes amazing characters, and again she researches well. Though i feel i should point out some of her science(especially related to computer technology) IS off, but this is i believe more due to the age of the books, than to her not researching.
anyway some notable mentions:Fredrick Pohl, Robert Silverberg, Poul Anderson or well just about anyone published regularly in the good sci fi magazines. (like Issac Asimov's Science Fiction Magazine)
Anyway honestly im forgetting a few, one that is tickling my mind right now that i cant remember his books or name, but that is a great read....bah. should get you started.