I find the ironclad age fascinating for the incredible variety of types it generated. Between HMS Warrior and the Royal Sovereign class of 1892, the Royal Navy (and many others) built ships in twos or threes with sails, no sail, barbette guns, central battery guns, turreted guns, vanishing guns, low freeboard, high freeboard... almost any mix of characteristics you can think of. The Royal Sovereigns finally established the classic 'pre-dreadnought' layout which lasted until HMS Dreadnought appeared in 1906, and started the trend for the RN to build series of ships to identical designs, each type being a gradual improvement on the last (with the exception of the 2nd class colonial battleships and the 'semi-dreadnought' Lord Nelson' class).
I also find it fascinating that the US were the first to use ironclads in combat, then dropped out of naval construction almost completely for three decades. Neither of the designs that fought at Hampton Roads were widely replicated, the 'monitor' concept only re-appearing in the First World War as a vessel for shore bombardment rater than surface-to-surface combat.
For a short and very readable overview of developments between the launch of the first sea-going armoured warship Gloire in 1859 and the Battle of the Leyte Gulf, which marked the end of the battleship era, I would recommend Battleship by Peter Padfield. Prices from $18 for the new edition on Amazon.com to £2.85 for the old one (which I have) on Amazon.co.uk. Worth every penny IMHO 8)