There are about a gazillion salsa recipes out there, but the fact of the matter, the best and most versatile salsa probably is the simplest. It is called "salsa cruda" and I just throw it together in about 5 minutes.
I'm going to give you a "recipe" but you can vary the ingredients as you feel like
3 large ripe tomatoes, diced (I use the skins and cores and seeds)
1/2 sweet onion, peeled and diced
1 garlic clove, peeled and minced
1 serrano or green jalapeno pepper, seeded and finely diced
some fresh cilantro leaves, chopped (about 2 tablespoons)
juice of one ripe lime
pinch of salt
Combine all the ingredients in a bowl, and chill before serving.
Some people like to use or add red onion or green onion. Some use lemon juice.
Canned chilis are acceptable as well, though I like everything fresh.
This recipe is the basic salsa, which can then be modified with other ingredients, such as mango, pineapple, peach, fire-roasted tomato, etc.