General:
* Seasoning
* Spice
* Sauce
* Relish
* Topping
* Accompaniment
* Flavoring
Specific examples:
* Chutney
* Mustard
* Ketchup
* Mayonnaise
* Pickles
* Relish
* Salsa
Formal:
* Taste enhancer
* Flavoring agent
The best word will depend on the specific context. For example, if you are talking about a small jar of mustard, "condiment" is the most appropriate word. If you are talking about a large bowl of salsa, "topping" or "accompaniment" might be better choices.