Most of the Honor Harrington books are good (starting with On Baselisk Station), and I’m told David Weber’s other series are also worth reading.
Trading in Danger, by Elizabeth Moon, and the two sequels (so far) is also very good, and somewhat different in that it’s a military sci-fi book… about a civilian merchant captain trying to avoid getting caught up in a war (while of course, perusing that which is most important: Trade and Profit)
The Wing Commander books are all quite good, they start with either Freedom Flight or Action Stations (which is a prequel detailing the beginning of the Terran-Kilrathi War, as well as the beginning of future Admiral Geoffery Tolwyn’s military career)
Hoka, Hoka, Hoka! by Gordon Dickson and Poul Anderson is a book that starts off slightly goofy and silly, and progresses to higher and higher levels of absolute hystericaly funny comedy and parodizes various works of human literature and movies (including stories of cowboys and indians, pirates and sailors, Sherlock Holmse, James Bond, The French Foreign Legion, and the legend of Don Juan)