[Emperor's Child]

For the space-opera theme books.

I'd recommened "In Conquest Born" by CS Friedman. As I recall there are some good fleet battles in that one, some diplomatic intrigue, etc.

Old Classic of course is Starship Troopers by Heinlien..though that is more a commentary on society than than a good old space fight... But hey... Its humans versus bugs.. How much better can it get?

A new author I like is Peter F. Hamilton. He wrote a series of 6 books: Reality Disfunction (2 books), The Neucronium Alchemist (2 books), and the Naked God (2 books). The whole series is pretty good, and he did a few single books (The Nano Flower for one) I'd also recommend.

David Drake is a Sci-Fi author that writes in a Near future setting and he also gets deep into the guts of fighting. A solid "must read" if you like the space combat theme of SF.

The "Mote in God's Eye" series by Niven and Pournelle is another Very good read, actually. You have Mote, and then the gripping hand more recently, both of which are good. Both have lots of diplomacy and then fighting.

Nivin also did the Man-Kzin war series, too. They are another good old fashioned space scrum of man against Space Kitties (who kick human butt on more than one occasion as I recall).

Ringworld series (Niven again) is more of an exploratory type of read on, well, a ringworld. Interesting and it has some generic space fights.

Of course I could not make a recommended reading list without the Foundation series by Azimov. Gotta read that one in your lifetime if you are a serious SF reader.