There's also quite a few books written about the planets and secondary characters. "A Stitch in Time" and "The Never-Ending Sacrifice" are set on Cardassia. Then there's a three book set called "Worlds of Star Trek Deep Space Nine " set on each planet like Andor and Ferenginar.
There's a bunch of Klingon novels like "Left hand of Destiny" and the "Klingon Empire" book set.
The other strange one (in a good way) is "Rising Son." A weird book about Jake Sisko joining a group of space thieves. I swear I read it thinking Joss Whedon must have gotten his idea for Firefly out of it!