Master and Commander and Post Captain, by Patrick O'Brian. Post Captain, the second book in O'Brian's series of Napoleonic era British Navy novels featuring Jack Aubrey and Stephen Maturin, is considered by many to be the best of the series, and is often recommended as the book to read first. It is easy to see why: many of the recurring characters of the series are introduced here for the first time, as well as the seeds of many things that are resolved much latter.
I agree that it is one of the best books of the series, perhaps the best, but I do not think it ideal as an introduction to the series. Without the background given by Master and Commander I think that Post Captain is harder to follow and the relationship between Aubrey and Maturin much harder to understand. I think it is much better for the reader new to Aubrey and Maturin to begin with Master and Commander, a simpler (though not simple) book and to get a good feeling for the two and their world before tackling the lengthier and more involved Post Captain.
Certainly my own experience agrees with this course: I first read Post Captain in the early '90s, and found it a real struggle to finish. Perhaps a year later I found a copy of Master and Commander and was enthralled. I immediately re-read Post Captain and was further enthralled: in this re-reading the book pulled me in and carried me through the story in a state of eager concentration, much better prepared to see what the book had to offer.
Ashes of Victory and War of Honor, by David Weber. These books, the nineth and tenth of Weber's vastly popular science fiction novels about Honor Harrington, an officer in the Royal Navy of the Star Kingdom of Manticore, chronicle then events taking place after Harrington's return from imprisonment and presumed death, the downfall of the People's Republic of Haven, the reformation of the Republic of Haven, and the continuing tensions between Haven and Manticore. The Honor Harrington series are well written military science fiction, probably the best series of any of the current crop of this currently quite popular sub-genre.
Illium, by Dan Simmons. This novel, the first of two, is an interesting blend of mythology and science fiction, mixing a re- enactment of the Iliad (observed by academics re-embodied and recycled at the whim of the gods), the reawakening of a post-Post Human Earth, and the scrutiny and action of the robotic residents of the outer solar system into an interesting and engaging story. I'm looking forward to reading Olympos, the concluding book of the duology.
Captain Kilburnie, by William P. Mack. Mack is a retired U.S. Navy Vice Admiral and this is his first novel about Fergus Kilburnie, a young Scottish officer in the Napoleonic era British Navy. It was originally published by the Naval Institute Press. I enjoyed the book, although the last third seemed to lag, and am looking forward to reading the sequel.
Unicorn's Blood, by Patricia Finney. Intrigue and espionage in the London and Court of Queen Elizabeth I, this is excellent historical fiction with interesting characters, story, and an excellent recreation of Elizabethan England.
Otherness, by David Brin. A collection of Brin's short stories.