When I think of Renaissance, I think of Italy and it's almighty influence and power! Personally, I believe that Italy should have the greatest strengths technology wise and economically wise.
In aspects of military, Italy should have a strong militia based army, well equipped with pike, musket and especially sword.
Unit Suggestions
(some units might already be on the official list and this is only a suggestion)

SPECIAL UNITS
- svizzero guardia di palazzo (Swiss Guard) - armed with halberd
- lancia svizerro (Swiss Pikemen) - armed with pike and rapier

MEN AT ARMS
- Soldata di Ferrara (Ferraran Men at Arms(Mounted as well)- armed with medium sword and wooden shield (AVAILABLE AT EARLY PERIOD)
- Soldata da Ducato di Milano (Milanese Men at Arms(Mounted as well)- armed with rapier and buckler shield (AVAILABLE AT EARLY PERIOD)
- Soldata da Comune di Firenze (Florence Men at Arms(Mounted as well) - armed with rapier and buckler shield (AVAILABLE AT EARLY PERIOD)
- Arciere da Repubblica di Venezia (Renaissance Venetian Archers/ men at arms)- armed with rapier and composite bow (AVAILABLE AT EARLY PERIOD)
- Cavaliere D'Italia (Mounted Italian Knights) - Armed with Italian armour and rapier (AVAILABLE AT EARLY PERIOD)
- Early Soldata D'Italia (Combined Italian men at arms)- Armed with pike and rapier and armoured with medium/heavy armour. (AVAILABLE AT EARLY PERIOD)
- Soldata D'Italia (Combined Italian men at arms) - Armed with stronger pike and rapier and armoured with light/medium armour. (AVAILABLE AT MIDDLE PERIOD)
- Late Soldata D'Italia (Combined Italian men at arms) - Armed with stronger pike and rapier and armoured with light/medium armour (AVAILABLE AT LATE PERIOD)
- Fuciliere d'Italia (Riflemen)- armed with stronger musket than Italian Musketeers and basically no armour.


CAVALRY
- Pistola Arciere Cavalleria D'Italia (Mounted Gunners) - armed with cavalry pistol and short spear always. Armour depends on age and class.
- dragone nell'Arte Militare d'Italia (Italian Dragoons) (Early, Middle and High) - Armed with rapier always. Armour depends on age and class.

MILITIA
- Milizia d'Italia (Italian Militia) -armed with arquebusiers and medium armour (Early, Middle)
- Milizia da lancia d'Italia (Italian pike militia) - (Early, Middle)
- Late Milizia d'Italia- armed with muskets and light armour.
- Late Milizia da lancia d'Italia- Armed with pike and light armour.

Correct me if I have made any mistakes