Sergey Snegov wrote a pretty good space opera trilogy "Humans as Gods".
Strugatsky brothers (just don't read anything written solely by Boris after Arkady died, it's pretty clear who was the brain and who was the pen in the duo).
Kir Bulychev wrote absolute shitton of books and stories.
There's also polish ones, of course the giant Stanisław Lem, and less famous Janusz Zajdel (though i have mixed feeling about Zajdel, a lot of his stories were interpreted as anticommunist after 1989). Hidden gems are Krzysztof Boruń and Andrzej Trepka - their books are probably not translated to english and pretty forgotten in Poland since they wrote the real socialist sci-fi.