Tomswift2002 just named you three complete standalones. In my opinion though, and the opinion of a lot of other people here, the really amazing stuff TrekLit has going is the interconnected ongoing universe that has formed between the novels set after each series ends (post-What You Leave Behind, post-Endgame, post-Nemesis).
There's a flowchart in my signature that links together all the novels in this continuity. It looks huge, but don't be intimidated - you can pretty much start anywhere. It's meant to be a tool for you to figure out what to read next, or which books come before or after the one you're currently on, not an exhaustive list of everything you MUST read in THIS order, if that makes sense.
I recommend two popular starting places, based on what you've said. The Deep Space Nine relaunch begins with Avatar, and has a Jem'Hadar character I think you'll love. And the Destiny trilogy is the best Borg story ever told, and despite having a bunch of stuff preceding it, was designed as (and succeeds at being) a fantastic jumping-on point for the ongoing continuity. Just be prepared for some characters to not be in exactly the places you left them...
(As far as Data goes, you'll enjoy Immortal Coil and then the Cold Equations trilogy, but there's a lot of great stuff between Destiny and the Cold Equations trilogy, which I would honestly recommend reading. You can start with Cold Equations, too, if you want, but it's less smooth than starting with Destiny or Avatar.)
Bottom line: there is an insane amount of amazing TrekLit out there for you to find. Welcome!
