Beyond these six elemental factors, there are other ingredients you might consider adding to your salsa to make them more substantial or add a different element of flavor.
You can add cooked beans to a salsa to turn it into a more substantial side dish or "dips" for chips, especially if you want to make a light yet nutritious vegetarian meal or side dish. Black beans and black-eyed peas work especially well in such uses because of their delicate size and dramatic colors.
Peppers in a salsa don't have to be spicy; sweet bell peppers in a variety of colors can be added to bring an additional crisp and summer flavor to a salsa. You can also char the peppers over a grill or under a broiler to soften them and add a richer flavor.
Sugar or Honey
Some fruit-based salsas can benefit from a little extra touch of sweetness—even in lieu of adding any salt. I have sometimes found this to be the case with berry-based salsas and others where the sweet-and-spicy flavors need to take precedence over any savory elements. Always add such flavors slowly, tasting as you go just as you would add the salt. You don't want to overwhelm the salsa with sweetness, but sometimes it can help bring the right balance.
Yes, believe it or not some salsas can benefit from a judicious splash of spirits: rum, tequila, or perhaps a touch of bourbon. I especially like doing this when I'm serving the salsa as a topping on grilled meats, which may have been marinated with these same spirits in the mix.
Some salsas can benefit from the addition of other spices such as ground cumin, cayenne or black pepper, or even a touch of cinnamon. Just try not to add more than one or two additional spices to the basic mixture, and pick those that complement the other ingredients well.
Sometimes a salsa can benefit from a touch of olive oil as well, in order to held blend together the flavors and if it seems too "dry".