I've been reading Sci Fi for a looong time

, I can recommend more than a few "galactic empire" books:
Peter F. Hamiltonalmost all of his books (the one's I've read) seem to deal with Galactic EmpiresSeries: The Reality Dysfunction (really excellent read)
Pandora's Star and Judas Unchained
Fallen Dragon
Series: The Damned by Alan Dean Foster
(A Call to Arms, The False Mirror, Spoils of War)
Christopher B. Rowley: War for Eternity, The Black Ship, and Starhammer
Jack L. Chalker's Well of Souls series
Classics: Asimov's classic Federation series, Heinlein's Starship Troopers, L. Ron Hubbard's Battlefield Earth, Frank Herbert's Dune (series)
I'll add any more I think of, these are my favorites.