Felicia Day, an avid twitterer herself, compiled a Twitter Author List - what a great public service as these authors can be hard to find for oneself. Also this serves as an excellent case study of the power of twitter; in order to create her list, she reached out to her substantial twitter network to find out the twitter addresses of these authors. Together we know all that is known; twitter helps make that accessible.
My recommendations to follow are:
Someone let me know if George R R Martin starts twittering updates about A Dance With Dragons, ok?
Photo credit digitalbear.