Don Glut wrote:
I have to agree with Bill -- Bradbury's was/is the best-known science fiction writer. But I think I'd have to qualify that a bit, and add "to people who actually read books" (and how many do that anymore).

To the average kid-on-the-street playing some videogame on his I-phone or sending yet another text message, the most famous "sci-fi" writer could be someone like that guy who makes all those space-battle movies.
I think if one did poll average citizens and asked them to name a famous science fiction writer (and limited the responses to actual authors, not "George Lucas" or "Steven Spielberg"), I think the top three results would be Bradbury, Wells and Verne, followed by Asimov and Clarke.  Bradbury is helped, like I said, by his presence on school reading lists, and that he is frequently turned to when TV or print news outlets want a comment from a sci-fi author about something in the news.  Asimov and Clarke, when they were alive, got a lot of exposure by benefit of being science writers in addition to sci-fi writers, so they also turned up often on TV or consulted for print articles on scientific matters.

Although Michael Crichton was a best-selling author, I don't think his name would come up in the top 5 because of lot of people would classify him as a writer of "thrillers" and not sci-fi, in spite many of his books being sci-fi.  The logic of these people goes like this: (1) Science fiction is a lot of goofy, far-out stuff with rocketships, aliens and monsters, read by pimply-faced nerds; (2) I am not a pimply-faced nerd and do not read science fiction; (3) I do read Michael Crichton.  Conclusion: Therefore, Michael Crichton is obviously not a science fiction writer!