The Enterprise 1701-J was seen in 'Azati Prime'. Daniels pulled Archer to the future (2551) to witness the Battle of Procyon V, the final battle of a war between the Federation (which by that time, included the Klingons as a member) and a transdimensional race called the Sphere Builders, by the Federation. The ship Archer and Daniels watched this from was none of than the Enterprise J! While we didn't get an external view of the ship, we did get to see a display of the ship on the wall of the coridoor of the ship.


Beyond this, we have no real info about the ship. Considering the Federation appears to employ Dauntless classes at this point, we can conjectur that Quantom Slipstream might be the primary FTL drive. Phasers still seem to be a main weapon in the 26th century, since we saw the E-J fire one during the course of the battle. Other weapons and features are unknown.
On a related note: Someone at the Scifi-Mesh Forums is working on a 3D model of the E-J and someone else is working on one for Bridge Commander.
Also, I didn't take nor claim credit for the screen shots. Someone at the SF-Mesh forums posted them.






