David Brin has written quite a few novels by now, but my favorites are the Uplift series. In chronological order within the novels, these are: Sundiver, Startide Rising, The Uplift War, Brightness Reef, Infinity's Shore, and Heaven's Reach (on a side note, I love his titles, and the poetry in the books that they come from). They are not exactly light reading, but they're very well done if you like complicated plots.
In the future in which these are set, mankind has genetically altered both dolphins and chimpanzees (and are possibly going to add dogs to the list) to be more intelligent and capable of human speech. They managed to do this just before the other sentient beings in the universe discovered humanity's existence, which is the only thing that kept some of these other species from immediately taking humans in hand for some reengineering. Galactic culture is based on this proces of uplift, where more advanced races alter the genetics of proto-sentient races in a long chain back to the Progenitors. Because humanity uplifted two species before we were discovered, that gives us the status of patrons, rather than clients which can be altered in whatever manner the patron species chooses. Which leads to some messy Galactic politics, as some races are not happy at all about the status or presence of humanity, which is a "wolfling" species - a species whose patrons seem to have abandoned them. Which is where the novels begin.
It is not up to the level of the first trilogy, but i still enjoyed it. And it leads up to the 6th book which is, while not as deep as the first 3, still quite fun to read.