Originally posted by Singh
1. Tribbles!!
2. The one where M-5 took over the Enterprise.
3. Squire of Gothos
4. The doomsday machine
I REALLY loved the Vendetta book - one of Peter David's best works, second only to Q-squared and the one where Data becomes human (quite literally), but i forgot the name of the novel since its been so long since i saw it....
Q-Squared was also very good, true. I'm just a little soft when it comes to the pre-Voyager Borg (in Vendetta).

Metamorphosis, by Jean Lorrah. Also a good read, especially if you've already read the other book with the extra characters in it - Survivors, also by Jean Lorrah.
Other Trek books I thought were outstanding were:
My Enemy, My Ally - by Diane Duane (TOS)
Dreadnaught - by Diane Carey (TOS)
Strangers in the Sky - by Margaret Wander Bonanno (TOS)
Probe - by Margaret Wander Bonanno (TOS)
Prime Directive - by Judith and Garfield Reeves-Stevens (TOS)
Black Fire - by Sonni Cooper (TOS) (one of the oldest TOS novels)
Death Count - by L.A. Graf (TOS)
Q-In-Law - by Peter David (TNG) (some of the most hilarious scenes ever)
Imzadi - by Peter David (TNG)