Excellent SciFi reads
Dan Simmons - Hyperion series, Illium, and Olympos. The best Sci FI you will ever read hands down.
Orson Scott Card, Enders Game. The others in the series, and the Bean series are good books, however it is like comparing Dune to its Sequels, they all pale in comparison.
Robert A. Heinlein - Starship Troopers
Richard K. Morgan - Altered Carbon, Broken Angels, and Woken Furies. Market Forces and Black Man were ok books
Roger Zelazny - Lord of Light, this is perhaps one of the best books of all times, and is on par with the likes of Hyperion as far as quality of the read.
Peter F hamilton - The Commonwealth Saga (excellent space opera), Fallen Dragon, The Night's Dawn series are all reasonably good books.
Hannu Rajaniemi - The Quantum Thief
Larry Niven - A Mote in God's Eye, and to a less extent The Gripping hand. The ringworld series are also good.
Herbert - Dune, skip the other books, none of them even remotely compare.
John Scalzi - Old Mans War is excellent the rest of the seriers are ok.
There is one series with a good amount of space combat, but it' name fails me. I will put it in here once I remember.
If you Like Halo read Greg Bear - Cryptum