I've read a lot of Larry Niven over the years, and you can get a sense of his politics from this interview. I always felt that his story, The Cloak of Anarchy was particularly good.
I've never read any Dan Simmons except for this short story pointed out by another Freeper. That, this follow-up message, and messages on his forum are interesting reading. There is also some interesting stuff on Jerry Pournelle's site.
Michael Chrichton's speeches on subjects like Global Warming are definitely worth reading.
On Politically Incorrect years ago, Ray Bradbury went off on a rather passionate defense of Senator Bob Packwood, saying that by the standards used to push him out, Bradbury had sexually harassed his wife until she married him.
James P. Hogan apparently has some sympathy for Holocaust revisionists (see 22 February 2006 message). Not sure what that says about the rest of his politics.
Now, with respect to Harlan Ellison, I won't buy an Ellison book, not because of his leftist politics or the Rush Limbaugh joke ("What's the difference between the Hindenburg and Rush Limbaugh? One is a big Nazi gasbag...") but because he's a world class jerk. The angry little man won't be getting any of my money unless, of course, they release The Starlost on DVD.
I'm glad to see someone else visits Pournelles site, it's where I stole my tagline