Startide Rising - The best in David Brin's Uplift Wars novels, SR follows the adventures of a dolphin/human starship crew stranded on a deadly world as an interstellar war rages over their heads. Great extrapolation of how technologically advanced cetaceans might act and think; brilliantly realized extraterrestrials; and a believable planetary environment, thanks in part to Brin's background as an astrophysicist. Also a lot of rip-roarin' action.
On Stranger Tides - Pay no attention to Disney's use of the title for the POTC franchise. On Stranger Tides is vintage Tim Powers: a deeply weird, deeply logical, deeply occult and well researched take on pirates, voodoo, and the fountain of youth. It also moves faster than a gunboat under full sail.
Protector - Larry Niven's SF explanation of the nature of old age and human evolution. Overtaken by current discoveries in the human genome and the fossil record, but still a lot of fun, with a great space battle between two STL starships orbiting a dwarf star.