Below are a few links to my favorite authors and other Sci-Fi sites.
Robert Heinlein
Andre Norton
Eric Flint
David Weber
John Ringo
Mercedes Lackey
Roger Zelazny
Frank Herbert
SCI-FI LISTS - Top 100 Sci-Fi Books
Science Channel's Top 10 Sci Fi Books
Baen Books (I've read each of the books in their free Library more than once).
Open Culture's Free Sci Fi Classics
Free ebooks, bargain kindle books