If you ordered one of the Deluxe Digital Editions of STO, then you have access to a special Joined Trill. Here is the info on their special abilities, from here:
Hyper Metabolism (regular Trill have this too): +33% Toxic Resist, +33% Radiation Resist, +10% Health Regeneration
Description: Ground Trait. Constantly regenerates health and provides innate resistance to the effects of radiation and toxins.
Joined Symbiote: +3.3 Starship Energy Weapons Training, +3.3 Starship Projectile Weapons Training, +3.3 Starship Warp Core Training, +3.3 Starship Engineering Training, +6.7 Starship Operations Training
Description: Space Trait. The memories of your symbiote improve your abilities in a wide range of starship roles.
Rest of the thread seems to detail that the Joined Trill gets access to five bonus slots – so, basically, the Joined Symbiote is a free add on to a Trill character. Those stats look really sweet.
And, if you buy a lifetime subscription – you can play as a Liberated Borg. Their information is on the main site here. Regeneration looks really sweet, and Efficient is nice. I really dig both of those – a good space ability is always nice (I try to go with all space bonuses all the time, but that’s just me), and that ground ability would be really, really useful.
I just hope you can make a liberated Borg of any species.