Orson Scott Card is a genius. Few authors can do both Science Fiction and Fantasy, but Card pulled it off marvelously--although the Ender Saga takes a slight dip after "Speaker for the Dead", he more than makes up for it with his newer stories following Bean with "Ender's Shadow" and that series.
Personally, I've gravitated towards "Alvin the Maker", his Fantasy series. I haven't gotten a hold of the newest one ("The Crystal City), but I have yet to pick up a Card book I did not like.
As for suggestions of other Science Fiction books, Kage Baker (often published in 'Asimovs Science Fiction') wrote a series that starts with "In the Garden of Iden" that is a fascinating read, and Rick Cook wrote an amusing fantastic-comedy about a computer programmer brought into a magical world with "Wiz Biz" (hard to find, but it's free at
www.baen.com/library ).