Escarole! I adore it in soups and braises. Not curly escarole, which organic lettuce growers use mostly as a form of natural packing material.

Tarragon. You don't need it often, but when you do there is no substitute.

Rapini. You can sometimes find these tiny little bundles in the store for way too much money, but I NEED MOAR RAPINI!!!

My late mom used to call rapini a spring tonic.  She would buy it only in the spring, so deep was her commitment to the Italian ritual!  The feels.  :-/

I grow Texas tarragon, for the leaves and flowers.  French tarragon is milder but it just doesn't hold up to the high temperatures and humidity of Florida.  So far, it's perennial.

Dill. Again you don't need it all that often, but when you do there is no sub.

New Mexico green chiles. I roast and freeze them to make green chile stew in the depths of winter. They are a vegetable AND a flavoring!

how spicy?

The ones I get here are not very. Apparently some varieties are spicier than others.

Japanese edible chrysanthemum leaves aka shungiku. Excellent in chanko nabe!

Perilla. It's the leaf you often get with sushi, but also excellent to wrap grilled meats!

Bitter aka Seville orange. I use the juice to marinate Cuban pork roast, but it's very hard to find.