Feel free to suggest any other "great" ST books that have not already been mentioned.
Before Steve Mollmann's Novel Rankings
site went kaplooey, these were the top ten all-time best rated Star Trek novels:
- Uhura's Song by Janet Kagan
- Dwellers in the Crucible by Margaret W. Bonanno (aka "Garamet")
- Imzadi by Peter David
- The Wounded Sky by Diane Duane
- Strangers from the Sky by Margaret W. Bonanno
- Q-Squared by Peter David
- Catalyst of Sorrows by Margaret W. Bonanno
- A Stitch in Time by Andrew J. Robinson
- Immortal Coil by Jeff Lang
- Federation by Gar and Judith Reeves-Stevens
Of course, YMMV.