USS Excelsior NCC-2000
Originally a prototype NX vessel, the USS Excelsior is the first of her class. Originally fitted with a transwarp drive, it was later given a standard warp drive and given to Captain Hikaru Sulu. It then went on to play a pivitol role in the Khitomer Peace Accords, giving the Enterprise enough time to destroy the prototype bird of prey. The USS Dragon NCC-27749-A enountered the Excelsior, thought to be lost, near a temporal/dimensional rift.
I've always liked this ship since I first saw it in Star Trek III, and was very happy when it played a key role in Star Trek VI! I like the design almost as much as I like the Sovereign class.