1 large onion
6 medium tomatoes
6 bell peppers of various colors
Salt
Black pepper
White vinegar
Chop it up, mix it and let sit for a couple of hours before serving. I have found that if you serve right away, it will taste like it needs more salt, but if you add it, it will be too salty after a couple of hours. Also, don't forget that chips and Mexican food in general are pretty salty, so my advice is to err on the side of caution with the salt.
I leave one third of the batch as listed above (mild), to one third I add a finely chopped green chile (medium) and to the final third I add half a haber�ero (hot) chopped super fine as you don't want a big chunk of that pepper in one bite. This year with all the rain, the tomatoes are very watery and the peppers seems smaller than I recall, neither of which is optimal, but it doesn't matter in terms of taste. Roma tomatoes are a good substitute but my local farm doesn't grow those and getting the freshest produce makes a huge difference. The more moisture in the tomatoes, the coarser you have to chop the ingredients or you will end up with salsa soup.
I have made it before with garlic and that was good too. Best thing about the recipe is if you have a knife and a bowl, you can make it.
As for uses, it is obviously great as a dip or added as a topper on any Mexican meal, but it also livens up salads and my favorite use is in an omelet with a strong cheddar cheese.