"Best Destiny" by Diane Carey (Pocket Books, 1993). "A beautiful imagining of Kirk's childhood and how it shaped him to love the stars."
"Spock's World" by Diane Duane (Pocket Books, 1988). "If Mr. Spock is your favorite character, this is amust read. The relationship he forges with Dr. McCoy finally gets the nuanced treatment it deserves."
"Prime Directive" by Judith and Garfield Reeves Stevens (Pocket Books, 1990). "One of the best incarnations of the original bridge crew, with every character given equal consideration and full development, against the backdrop of a real-deal science fiction story."
"Ex Machina" by Christopher L. Bennett (Pocket Books, 2004) "A great example of how a 'Trek' novel can fit within 'canon' while existing between the movies we love."