[ATDrake]

If you like the older series, Diane Duane's books are very good indeed and you can get some of them bundled into cost-saving omnibus editions.

Peter David was also a very good writer from what I read of his TNG Star Trek novels*. And John M. Ford's How Much for Just the Planet? is the funniest Trek novel I've ever read. His other Klingon-based book which I've not read is widely considered classic, as well.

* The ones that were packaged as "specials" like Vendetta and Imzadi and Q-Squared tend to be of higher quality and more imaginative/enjoyable storylines than the regular "numbered" series books, which were also mostly good, but not at the same level.