Robert L. Forward for hardcore science fiction. He did an excellent job of combining interesting science with interesting narratives and characters.

James Alan Gardner for more traditional science fiction. The second book in his League of Peoples series is a bit weak in my opinion, but even so it's my favorite science fiction series.

I don't know if either will cause you to run for a dictionary, but Forward's novels may cause you to flip through some science text books, and I greatly enjoyed the manner that Gardner put forward many of his "big ideas."