While I really love what's been going on with the Trek-lit books post-Nemesis
, there are quite a few gems from the 1980s and 1990s. King Daniel posted some classics above, and I'd also like to mention The Final Reflection, How Much for Just the Planet?, Dragon's Honor,
the McIntyre novelizations of The Wrath of Khan, The Search for Spock,
and The Voyage Home, The Wounded Sky, Crisis on Centaurus, Doctor's Orders, Q-in-Law, Fallen Heroes,
and The Captain's Daughter
as being some older Trek-lit works that are worth reading, all published before 1997.
I do think the Trek-lit line suffered from about 1993 through 2005 from too many books published per year, but that's not to say there weren't some gems published during that period. I also think it's helped that the authors are perhaps not so bound as they once were with regards to the various series and characters, since there are no TV or film works in the foreseeable future for the "Prime Universe", which allows for major changes for established characters - you couldn't do much of that in the 1990s with TNG, DS9, and VOY all on TV during that period.