Other civilizations include Byzantines (Paladins, Heavy Camels, Hussars, Cavalry Archers, and their Unique Unit the Cataphact- they'd be right up with the Persians but they lack Blast furnace which makes their units attack for less), Mongols (awesome Hussars with extra hit points, and awesome cavalry archers, Heavy Camels, but no Paladins), and Saracens (extra hit point Heavy Camels, Hussars, Cavalry Archers, Unique Unit Mameluke, but no Paladins). If you like Cavalry, Persians have to be the best civilization for you hands down.

I also believe they have all cavalry related technology upgrades. Persians have the best cavalry as a civilization, Hussars, Paladins, Heavy Camels, Calvary Archers, and even their Unique Unit the War Elephant is listed as a cavalry unit. So really they don't have that great of a cavalry arsenal, however because their Paladins are so awesome they are probably higher up the chain than say, Turks, which have Hussars and Heavy Camels but lack the Paladin. Franks have awesome Paladins but no camels or hussars.

Important to note that the OP is asking for civilizations with the best cavalry, not a single cavalry unit.

Age of empires 2 paladin