How about HMS Dreadnought, the first all big gun battleship built?
Not only was she the first all big gun battleship, but she was the first large warship to use steam turbines. She also was the only battleship to sick an enemy vessel during wartime by ramming (rammed a U-boat during WWI, the only enemy she ever sank).
USS Olympia, Dewey's flagship at the Battle of Manila Bay. Currently a museum ship in Philadelphia, its the oldest steel warship still afloat.
USS Fulton II--World's first steam warship
La Gloire--First Ironclad
HMS Warrior--First British iroclad, response to La Gloire
Great Eastern--Built in the late 1850's (?), capable of carrying nearly 5000 passengers. Failure as a passenger ship, but successful as a cable layer. Was the largest ship in the world for nearly 30 years.
CSS Hunley--Confederate submersible. First submarine to sink an enemy vessel in combat.