Genoese Crossbow Militia.

Available from a Large Town, lethal missile damage and infuriatingly tough to destroy. Oh, and don't forget armour piercing.

Portuguese Arquebusiers.

Easy to build (for gunners), devastating missile attack and able to face down enemy archers or survive a quick melee better than most gunpowder units.

Vardariotai.

Elite armoured horse archers, who despite being essentially bow-armed heavy cavalry, are fast moving and available from a wooden castle.