I'm of wallcraft's opinion, Baen doesn't really have cyberpunk or hard SF authors like those you mentioned. Still, here's my recommendations in addition to those mentioned.
- Tinker by Wen Spencer (not in Free Library but available on Baen CDs).
- Mother of Demons by Eric Flint.
- Mutineer's Moon, and The Apocalypse Troll by David Weber.
- Sheepfarmer's Daughter by Elizabeth Moon.
- A lot of Keith Laumer's books are available in Free Library. My favorites are Dinosaur's Beach (included in Odyssey) and The Great Time Machine Hoax (from The Lighter Side).
Check also
Baen CDs for additional free Baen books.