My favorite authors:

Rick Riordan
J.K. Rowling
Tui T. Sutherland
Jeff Kinney

I am now following them on twitter with the exception of Tui Sutherland who does not have a twitter account.

My favorite website is Tui Sutherland's, because she has a video about dragons.
http://tuibooks.com/wordpress/

Second is Rick Riordan's website, because of its design.
http://www.rickriordan.com/home.aspx

Third is J.K. Rowling, because is very interactive and has a magical tinge to it.
http://www.jkrowling.com/en_US/

Last is Jeff Kinney's.  It is a funny website, though.
http://www.wimpykid.com