Not exactly a species, but pre-singularity Ellimist and Crayak are my favorites, in terms of concept.
Before they ascended to mystical wishy-washy spacetime godhood, these two were technological marvels who transcended biological existence by yoking their fragile physical selves to titanic machine constructs of glass and steel and chained lightning; they commanded fearsome arsenals bristling with weapons that could tear stars in half with a single shot, or reduce planets to scattered ashes in a single blast; they wove in and out of real space with impunity, and had mastered faster-than-light travel to a degree beyond any other species of the galaxy.
Then they fell into a black hole, and the wondrous machine-gods became funky non-corporeal consciousness thingies wedded to the very fabric of spacetime itself...or something. Eh.
One thing Animorphs is really missing, as a sci-fi series, is sublime moments of geek static technowank. I like my phasers and my anti-entropy fields and my coherent neutronium whips and my quantum-computed Turing machines running a hypercubic chess match in four dimensions while modified tesseract-capable Langton's ants wander about changing the binary nature of the chess cells mid-game.
Pre-singularity Ellimist and Crayak are the closest the series comes to embodying that concept, though The Ellimist Chronicles was sadly lacking in specifics.
